Reveals the build fail fixed in the last hunk. Also prep work.

v2: name it i915 instead of dev_priv (Michal)
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/8e02dcf1b85462d17e96fb183440dd90261b7411.1545920737.git.jani.nikula@intel.com