Looking to our git log we can see that the most common case
is the update of the single i915_drm.h file.

There are some advantages of doing this standalone update:

1. Make reviews easier without the noise of other headers.
2. Avoid the developer to have to touch other areas that are
   not immediately related to targeted work.

Cc: Petri Latvala <petri.latvala@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Petri Latvala <petri.latvala@intel.com>