investigate ARM_GNU toolchain bare metal target

[jyao1]

Currently, we added ARM_GNU toolchain - https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads, with 11.2-2022.02: GNU/Linux target (arm-none-linux-gnueabihf, aarch64-none-linux-gnu).

The ARM_GNU also supports bare-metal target (arm-none-eabi, aarch64-none-elf).

This issue is to investigate if we can enable ARM_GNU bare-metal target (ARM_GNU_BAREMETAL), and if there is any size benefit.