drm/panthor: Fix NULL pointer dereference on panthor_fw_unplug

drm/panthor: Fix NULL pointer dereference on panthor_fw_unplug

This patch removes the MCU halt and wait for halt procedures during
panthor_fw_unplug() as the MCU can be in a variety of states or the FW
may not even be loaded/initialized at all, the latter of which can lead
to a NULL pointer dereference.

It should be safe on unplug to just disable the MCU without waiting for
it to halt as it may not be able to.

Fixes: 514072549865 ("drm/panthor: Support GLB_REQ.STATE field for Mali-G1 GPUs")
Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Karunika Choo <karunika.choo@arm.com>
Reviewed-by: Liviu Dudau <liviu@dudau.co.uk>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patch.msgid.link/20251215203312.1084182-1-karunika.choo@arm.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>