drm/amdgpu: updated host to psp mailbox cmd (v2)

added host to psp cmd for register list

v2: update to new interface (Alex)

Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: John Clements <john.clements@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>