drm/i915/icl: Handle rps interrupts without irq lock

Unlike previous gens, we already hold the irq_lock on
entering the rps handler so we can't use it as it is.

Make a gen11 specific rps interrupt handler without
locking.

v2: return early (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190410132124.21795-1-mika.kuoppala@linux.intel.com