[TF-M] Adding platform support for ArmChina Alcor AN557 MPS3 board

Hi I'm working on Adding Platform support for ArmChina Alcor AN557 MPS3 FPGA board . The code has been passed tfm_regression_test on AN557 fpga image and now submit to TF-M git repo. See: https://review.trustedfirmware.org/c/TF-M/trusted-firmware-m/+/27267

Could you have a code review on these code ? Any comments and suggestion are welcomed. Thank you! B,R Jidong