drm/amdgpu: Revised PSP comments

Revised comments in PSP SOS/Sysdriver loading sequence

Signed-off-by: John Clements <clements.jm@gmail.com>
Signed-off-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>