drm/i915: Restore lost "Initialized i915" welcome message

drm/i915: Restore lost "Initialized i915" welcome message

A side effect of removing the midlayer from driver loading was the loss
of a useful message announcing to userspace that i915 had successfully
started, e.g.:

	[drm] Initialized i915 1.6.0 20160425 for 0000:00:02.0 on minor 0

Reported-by: Timo Aaltonen <tjaalton@ubuntu.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Fixes: 8f460e2c78f2 ("drm/i915: Demidlayer driver loading")
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: drm-intel-fixes@lists.freedesktop.org
Link: http://patchwork.freedesktop.org/patch/msgid/20160825072314.17402-1-chris@chris-wilson.co.uk
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
(cherry picked from commit bc5ca47c0af4f949ba889e666b7da65569e36093)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>