drm/i915: Reject commands that explicitly generate interrupts

The driver leaves most interrupts masked during normal operation,
so there would have to be additional work to enable userspace to
safely request/receive an interrupt.

v2: trailing commas, rebased

Signed-off-by: Brad Volkin <bradley.d.volkin@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>