drm/i915: Organize plane register writes into tighter bunches

drm/i915: Organize plane register writes into tighter bunches

Pull all the plane register writes closer together to avoid having
a lot of unrelated stuff in between them. This will make things more
clear once we'll grab the uncore lock around the entire bunch. Also
in the future we might even consider moving more of the register
value computation out from the plane update hooks. This should make
that easier to do.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170309154434.29303-4-ville.syrjala@linux.intel.com
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>