Docs: Design of the TF-M isolation HAL

Add the TF-M isolation HAL API design.

Change-Id: I7f597b2502e44fcc197b47232dc1141e5a08fb8d
Signed-off-by: Edison Ai <edison.ai@arm.com>
Co-Authored-by: Kevin Peng <kevin.peng@arm.com>
1 file changed