drm/i915: add PLL enable/disable functions

For pre-ILK only.  Saves some code in the CRTC enable/disable functions
and allows us to check for pipe and panel status at enable/disable time.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
1 file changed