drm/amdgpu: add RAP TA header file

The RAP TA contains tests used to verify if
RAP(Register Access Policy), or otherwise known
as Security Policy is applied correctly
by PSP BL&TOS.

The RAP test is a measure to ensure that we reduce
the avenue of complexity and mistakes when dealing
with RAP in post-si execution, where debugging failures
related to RAP is quite difficult and expensive.

v2: add introduction for RAP TA

Signed-off-by: Wenhui Sheng <Wenhui.Sheng@amd.com>
Reviewed-by: Guchun Chen <Guchun.Chen@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>