drm/amdgpu: Change a few function names

Function name "psp_np_fw_load" is not proper as people don't
know _np_fw_ means "non psp firmware". Change the function
name to psp_load_non_psp_fw for better understanding. Same
thing for function psp_execute_np_fw_load.

Signed-off-by: Oak Zeng <Oak.Zeng@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian Konig <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>