Nuvoton: Enable no HXT/LXT configurabiliy ...

LXT/HXT are external crystl oscillator and can be absent on custom board.
This enables configuring LXT/HXT presence:
1.  By default, LXT/HXT are configured to be present, except M252 which has no HXT.
2.  When LXT is configured to not present, lp_ticker/watchdog will clock by LIRC instead.
3.  Limitations:
    (1) On all targets, LIRC-clocked lp_ticker gets inaccurate and fails to pass tests.
    (2) On NUC472/M453, HIRC-clocked PLL doesn't output 1MHz-aligned frequency. us_ticker gets slight inaccurate.
    (3) On all targets, LIRC-clocked RTC is not supported due to no H/W path/RTC clock source reset to LXT on reset/RTC not trimmed for other clock rates.
4.  On M263, TRNG's clock source defaults to LXT and needs special handling without LXT.
5.  On M252, replace target.hxt-enable with target.hxt-present for consistency.

To keep proprietary BSP DutyCycle definition and rename HighDutyCycle in extend API

Support M251/M261/M453/NANO130/NUC472 PWM duty cycle range as 0 ~ 10000

CMake nuvoton: fix ARMClang linker script command

stack: armc: Workaround config passing bug ...

Workaround a bug where the boot stack size configuration option is not
passed on to armlink, the Arm Compiler's linker. Prefer
MBED_CONF_TARGET_BOOT_STACK_SIZE if present, as this is what the
configuration system should provide. Fall back to MBED_BOOT_STACK_SIZE
if MBED_CONF_TARGET_BOOT_STACK_SIZE is not defined, as in the case of
buggy tools. If both MBED_CONF_TARGET_BOOT_STACK_SIZE and
MBED_BOOT_STACK_SIZE are not defined, then we fall back to a hard-coded
value provided by the linkerscript. See
https://github.com/ARMmbed/mbed-os/issues/13474 for more information.

Use boot stack size from config system ...

To allow overriding of the boot stack size from the Mbed configuration
system, consistently use MBED_CONF_TARGET_BOOT_STACK_SIZE rather than
MBED_BOOT_STACK_SIZE.

Fixes #10319

M453: Support bare metal ...

Relevant modifications to make TOOLCHAIN_* directories clear:
1. Remove TOOLCHAIN_ARM_STD
2. Rename TOOLCHAIN_ARM_MICRO to TOOLCHAIN_ARM

M453: Make memory specification configurable

NUMAKER_PFM_M453: keep __vector_handlers symbol in LTO builds ...

Add a "used" attribute to __vector_handlers to fix ARMC6 build with
the "-flto" flag.
(Error: L6236E: No section matches selector - no section to be FIRST/LAST.)

This attribute, attached to a function/variable, means that code must be emitted
for the function even if it appears that the function is not referenced.

Nuvoton: Support dynamic heap configuration on IAR ...

On IAR, configure heap to 1KiB at a minimum and expandable, dependent on available SRAM. This requires IAR 8.x.

Support targets:
-   NUMAKER_PFM_NUC472 w/ and w/o XRAM
-   NUMAKER_PFM_M453
-   NUMAKER_PFM_M487/NUMAKER_IOT_M487
-   NUMAKER_IOT_M263A
-   NUMAKER_M252KG

Guard RAM start and size defines

Target_NUVOTON: Add ARM_LIB_STACK and ARM_LIB_HEAP section ...

Instead of user defined symbols in assembly files or C files,
use linker scripts to add heap and stack - this is inconsistent
with ARM std linker scripts

Target_Nuvoton: Remove target specific implementation of _sbrk

[Nuvoton] Support boot stack size configuration option

Nuvoton: Fix alignment of execute region to 8-byte boundary ...

--legacyalign, --no_legacyalign are deprecated from ARMC6 compiler, in order to
remove deprecated flags all linker files (GCC and IAR as well to have uniformity)
should strictly align to 8-byte boundary

Remove uVisor from mbed-os

Merge pull request #6985 from OpenNuvoton/nuvoton_fix_rtosless_heap ...

Fix heap base/limit error with ARM_LIB_STACK/ARM_LIB_HEAP in RTOS-less

[Nuvoton] Replace __wrap__sbrk with overriding _sbrk ...

With _sbrk being weak, we can override it directly rather than #if to support heap with
two-region model.

[Nuvoton] Merge multiple ARM/ARMC6 sys.cpp into one

Correct Nuvoton compiler detection logic

Enable Compiling with ARMC6 across all targets ...

remove duplicate sys.cpp

[NUC472/M453] Remove mbed_sdk_init_forced() ...

1. With mbed OS 5, mbed_sdk_init() is ensured to call before C++ global object constructor.
2. Refine startup file with GCC_ARM toolchain related to this modification.

[NUC472/M453] Move SystemInit() to register unlock range for perhaps future protected register access

[NUC472/M453] Fix region end address error with IAR toolchain

CMSIS5: Replace target defined NVIC_Set/GetVector with CMSIS implementation

[NUC472/M453] Fixed scatterAssert of ROM limit

[NUC472/M453] Support bootloader

[NUC472/M453] Change sbrk() allocation to be 32-byte aligned

Merge pull request #3365 from OpenNuvoton/nuvoton_usb ...

[NUC472/M453] Support USB device

[NUC472/M453] Fix GCC warnings