Docs: Design of the TF-M HAL overview

Add the TF-M Hardware Abstraction Layer(HAL) overview.

Change-Id: I25246d05a3b0fd79f67836ed7191d16c0128e53c
Signed-off-by: Edison Ai <edison.ai@arm.com>
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
2 files changed