drm/amdgpu: always sending PSP messages LOAD_ASD and UNLOAD_TA

We allow sending PSP messages LOAD_ASD and UNLOAD_TA without
acquiring a lock in drm_dev_enter during driver unload
because we must call drm_dev_unplug as the beginning
of unload driver sequence.
Added WARNING if other PSP messages are sent without a lock.
After this commit, the following commands would work
 -sudo modprobe -r amdgpu
 -sudo modprobe amdgpu

Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Reviewed-by Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>