intel: Merge latest i915_drm.h

The main incentive to do this is to get I915_PARAM_REVISION.

v2: Rebase on top of some changes that were made to the header without
    copying the whole file from the kernel source.

Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Neil Roberts <neil@linux.intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>