drm/amdgpu: validate userq input args

This will help on validating the userq input args, and
rejecting for the invalid userq request at the IOCTLs
first place.

Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>