drm/panthor: Extend VM locked region for remap case to be a superset

drm/panthor: Extend VM locked region for remap case to be a superset

In the event of an sm_step_remap() that leads to a partial unmap of a
transparent huge page, the new locked region required by an extended unmap
might not be a superset of the original one. Then, if it leaves a portion
of the initially requested one out, the ensuing map will trigger a warning.

Fixes: 8e7460eac786 ("drm/panthor: Support partial unmaps of huge pages")
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patch.msgid.link/20260408191228.537625-1-adrian.larumbe@collabora.com
Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>