drm/panthor: Implement soft reset via PWR_CONTROL

drm/panthor: Implement soft reset via PWR_CONTROL

Add helpers to issue reset commands through the PWR_CONTROL interface
and wait for reset completion using IRQ signaling. This enables support
for RESET_SOFT operations with timeout handling and status verification.

Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Karunika Choo <karunika.choo@arm.com>
Link: https://patch.msgid.link/20251125125548.3282320-6-karunika.choo@arm.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>