drm/panthor: Add architecture-specific function operations

drm/panthor: Add architecture-specific function operations

Introduce architecture-specific function pointers to support
architecture-dependent behaviours. This patch adds the following
function pointers and updates their usage accordingly:

- soft_reset
- l2_power_on
- l2_power_off

Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Karunika Choo <karunika.choo@arm.com>
Link: https://patch.msgid.link/20251125125548.3282320-3-karunika.choo@arm.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>