drm/imagination: Disallow exporting of PM/FW protected objects

drm/imagination: Disallow exporting of PM/FW protected objects

These objects are meant to be used by the GPU firmware or by the PM unit
within the GPU, in which case they may contain physical addresses.

This adds a layer of protection against exposing potentially exploitable
information outside of the driver.

Fixes: ff5f643de0bf ("drm/imagination: Add GEM and VM related code")
Signed-off-by: Alessio Belle <alessio.belle@imgtec.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20251208-no-export-pm-fw-obj-v1-1-83ab12c61693@imgtec.com
Signed-off-by: Matt Coster <matt.coster@imgtec.com>