drm/panthor: Pass an iomem pointer to GPU register access helpers

drm/panthor: Pass an iomem pointer to GPU register access helpers

Convert the Panthor register access helpers to take an iomem pointer
instead of a panthor_device pointer.

This makes the helpers usable with block-local registers instead of
routing all accesses to go through ptdev->iomem. It is a preparatory
change for splitting the register space by components and for moving
callers away from cross-component register accesses.

No functional change intended.

v3:
- Pick up R-bs from Liviu and Steve
v2:
- Pick up Ack from Boris.

Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Acked-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Karunika Choo <karunika.choo@arm.com>
Tested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patch.msgid.link/20260427155934.416502-2-karunika.choo@arm.com