drm/amdgpu: Optimize RAS TA initialization and TA unload funcs

1. Save TA unload psp response status
2. Add RAS TA loading status check for initializaiton
3. Drop RAS context teardown to allow RAS TA to be reloaded

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>