drm/i915: Initialize the PPS HW before its first use

The initial DPCD read for eDP detection involves using the PPS, but so
far we only initialized the PPS registers after the DPCD read. The
reason this was done so far is to preserve a possible LVDS PPS HW setup
if LVDS is detected but eDP is not. This is not an issue any more after
the previous patch, so we can move the init earlier now.

This was caught by CI with the PPS sanity checks in place and the
initial eDP DPCD readout waiting for the panel power cycle timeout
without the PPS registers being initialized.

CC: Ville Syrjälä <ville.syrjala@linux.intel.com>
CC: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1466499109-20240-3-git-send-email-imre.deak@intel.com