drm/panthor: Clean up 64-bit register definitions

drm/panthor: Clean up 64-bit register definitions

With the introduction of 64-bit register accessors, the separate *_HI
definitions are no longer necessary. This change removes them and
renames the corresponding *_LO entries for cleaner and more consistent
register definitions.

Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Karunika Choo <karunika.choo@arm.com>
Link: https://lore.kernel.org/r/20250606101835.41840-3-boris.brezillon@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>