drm/panthor: Always use the IRQ-safe variant when acquiring the fence lock

drm/panthor: Always use the IRQ-safe variant when acquiring the fence lock

Since dma_fence objects can be shared with other subsystems, they may be
accessed from hardirq context in those drivers, and we have to take
that into account by also using the IRQ-safe variant when acquiring
the lock.

While at it, switch to the guard model.

Fixes: de8548813824 ("drm/panthor: Add the scheduler logical block")
Reported-by: sashiko-bot@kernel.org
Closes: https://sashiko.dev/#/patchset/20260625-panthor-signal-from-irq-v5-0-8836a74e0ef9@collabora.com?part=11
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-v1-1-b67ed973fea6@collabora.com