drm/panthor: Use a local iomem base for PWR registers

drm/panthor: Use a local iomem base for PWR registers

Add a PWR_CONTROL-local iomem pointer to struct panthor_pwr and switch
power controller register accesses to that base.

Update IRQ-local iomem base to use PWR_CONTROl-local iomem and update
the register definitions so the PWR block can be addressed relative to
its local base. This removes the remaining dependence on the global
device MMIO mapping for PWR register accesses. Update
panthor_gpu_info_init() to also use the correct PWR_CONTROL iomem for
the *_PRESENT registers.

No functional change intended.

v3:
- Clean up definitions for pwr->iomem and pwr->irq.iomem.
- Update PWR_INT_BASE to be relative to pwr->iomem.
v2:
- Update panthor_gpu_info_init() to use block-local iomem pointer.

Signed-off-by: Karunika Choo <karunika.choo@arm.com>
Acked-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patch.msgid.link/20260427155934.416502-7-karunika.choo@arm.com