Add targets subdirectory to high level CMake configuration file and
create new configurations for MCUs and individual targets. Change the
interpreter in the ARM scatter file to armclang, which is required for
CMake. Remove private and public interfaces in emac target
configuration. Ensure that all targets build on the arm gcc compiler and
arm compiler.

In case of unusing RTOS, IRQ handler executes "while(1)" and it causes a program freeze.
Therefore, I revised this processing. Also I added the heap setting processing and set the align to 8 byte.

For Arm toolchain build, Mbed 2(classic) programs occur an unexpected error if there is "#include "mem_XXXX.h"" in the script file.
It seems that the linker script can't find the include file because "mem_XXXX.h" file is not in the same path with the linker script.
(Refer to Issue #6975.)
To address this issue, I remove inclusion processing and define the related macros at ARMCC linker script file.

--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

The mainly changes is below:
- Update scatter file, linker file for bootloader support
- Update the file for RZ/A1 serial flash boot loader
- Add "device name" and "bootloader_supported" in targets.json

The mainly changes is below:
- Add flash_api.c
- Add the definition of SPI multi I/O Bus controller that is used for flash access
- Add "FLASH" as device feature
- Add the macro regarding information of the incorporated Flash
- Add the processing to expand code to RAM

For supporting to CMSIS5/RTX5, I added the start-up processing of 3 toolchains (ARMCC, GCC_ARM, IAR) and the register definition of RZ/A1LU specific.
In addition, I added the linker script files to implement the dynamic HEAP the same as GR-PEACH(RZ/A1H).