drm/i915: Unlock PPS registers after GPU reset

Reapply the PPS register unlock workaround after GPU reset on platforms
where the reset clobbers the display HW state. This at least gets rid of
the related WARN during LVDS encoder enabling on PNV.

Fixes: ed6143b8 ("drm/i915/lvds: Restore initial HW state during encoder enabling")
Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1473847453-4771-1-git-send-email-imre.deak@intel.com


Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
(cherry picked from commit 51f59205)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>