drm/drv: Add drmm managed registration helper for dmem cgroups.

Drivers will need to register dmem regions at probe time, so let's
give them a drm-managed helper.

Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20241204134410.1161769-3-dev@lankhorst.se


Signed-off-by: Maxime Ripard <mripard@kernel.org>