drm/panthor: Kill lock_region()

drm/panthor: Kill lock_region()

The meat in lock_region() is about packing a region range into a
single u64. The rest is just a regular reg write plus a
as_send_cmd_and_wait() call that can easily be inlined in
mmu_hw_do_operation_locked().

v2:
- New patch

v3:
- Don't LOCK is the region has a zero size

v4:
- Collect R-b

Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://patch.msgid.link/20251128084841.3804658-3-boris.brezillon@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>