1. Add a function pointer structure ta_funcs to psp context
2. Make the interfaces generic to all TAs
3. Leverage exisitng TA context and remove unused functions
4. Fix return code bugs

v2: Add comments for ta funcs macros and correct typo
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Candice Li <candice.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>