drm/i915: Program FW_BLC_SELF on 915G as well

drm/i915: Program FW_BLC_SELF on 915G as well

According to Bspec FW_BLC_SELF exists on 915G also. Let's program it.
The only open question is whether there's is a memory self-refresh
enable bit somewhere as well. For 945G/GM it's in FW_BLC_SELF, for
915GM it's in INSTPM. For 915G I can't find one in the docs. Let's drop
a FIXME about this, in case someone with the hardware is ever bored
enough to look for it.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1469804222-12650-2-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>