drm/i915: Be more careful when picking the initial power sequencer pipe

Try to make sure we find the power sequencer that the BIOS used
by first looking for one which has the panel power enabled, then
fall back to one with VDD force bit enabled, and finally look at
just the port select bits. This should make us pick the correct
power sequencer when the BIOS has already enabled the panel.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
[danvet: Shorten the vlv_intial_pps_pipe to make lines fit into 80
chars.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>