drm/panthor: Unlock the locked region before disabling an AS

drm/panthor: Unlock the locked region before disabling an AS

An AS can be disabled in the middle of a VM operation (VM being
evicted from an AS slot, for instance). In that case, we need the
locked section to be unlocked before releasing the slot.

v2:
- Add an lockdep_assert_held() in panthor_mmu_as_disable()
- Collect R-bs

v3:
- Don't reset the locked_region range in the as_disable() path

Fixes: 6e2d3b3e8589 ("drm/panthor: Add support for atomic page table updates")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patch.msgid.link/20251203121750.404340-4-boris.brezillon@collabora.com