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.

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

Adding a new target of HW development kit using [Samsung Exynos i S111](https://www.samsung.com/semiconductor/minisite/exynos/products/iot/exynos-i-s111/) module to Mbed-OS.
This will widen the HW choices of Mbed-OS enabled NB-IoT, GNSS and Security (eFuse, AES, SHA-2, PKA, Secure Storage, Security Sub-System, [PUF](https://en.wikipedia.org/wiki/Physical_unclonable_function)) modules.
Target Name: S5JS100

Co-authored-by: Ivan Galkin <ivan.galkin@samsung.com>
Co-authored-by: Seokwon Lee <swon.lee@samsung.com>
Co-authored-by: Zhizhe Zhu <zhizhe.zhu@samsung.com>
Co-authored-by: Xinyi Zhao <xinyi.zhao@samsung.com>