drm/i915: panel power sequencing for VLV eDP v2

PPS register offsets have changed in Valleyview.

v2: don't clobber port select bits on VLV when fixing up PPS timings
    don't bother with G4x PPS regs (Jani)

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Gajanan Bhat <gajanan.bhat@intel.com>
Signed-off-by: Vijay Purushothaman <vijay.a.purushothaman@intel.com>
Signed-off-by: Ben Widawsky <benjamin.widawsky@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>