drm/i915: fix drm_i915.h include grouping and sorting

Group and sort includes in i915_drv.h similar to other places.

Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/679923380d4757fed4e3a4c4bed80e40b9fdaeec.1644507885.git.jani.nikula@intel.com