drm/radeon: check PS, WS index

Theoretically, it would be possible for a buggy or malicious VBIOS to
overwrite past the bounds of the passed parameters (or its own
workspace); add bounds checking to prevent this from happening.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3093


Signed-off-by: Alexander Richards <electrodeyt@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>