drm/i915/perf: fix perf enable/disable ioctls with 32bits userspace

The compat callback was missing and triggered failures in 32bits
userspace when enabling/disable the perf stream. We don't require any
particular processing here as these ioctls don't take any argument.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: eec688e1

 ("drm/i915: Add i915 perf infrastructure")
Cc: linux-stable <stable@vger.kernel.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171024152728.4873-1-lionel.g.landwerlin@intel.com