drm/i915: Remove LVDS and PPS suspend time save/restore

In the preceding patches we made sure that:
- the LVDS encoder takes care of reiniting both the LVDS register
and its PPS
- the eDP encoder takes care of reiniting its PPS
- the PPS register unlocking workaround is applied explicitly whenever
the PPS context is lost

Based on the above we can safely remove the opaque LVDS and PPS save /
restore from generic code.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470827254-21954-6-git-send-email-imre.deak@intel.com