drm/panthor: Fix panthor_pwr_unplug()

drm/panthor: Fix panthor_pwr_unplug()

We can't call panthor_pwr_irq_suspend() if the device is suspended,
or this leads to a hang when the IOMEM region is accessed while the
clks are disabled. Do what other sub-components do and conditionally
call panthor_pwr_irq_suspend() if we know the PWR regbank block is
accessible.

Fixes: c27787f2b77f ("drm/panthor: Introduce panthor_pwr API and power control framework")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patch.msgid.link/20260625-panthor-misc-fixes-v1-7-b67ed973fea6@collabora.com