drm/amd/amdgpu: consolidate PSP TA unload function

Create common PSP TA unload function and replace all common TA unloading
sequences.

Signed-off-by: Candice Li <candice.li@amd.com>
Reviewed-by: John Clements <john.clements@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>