drm/i915: Get rid of intel_dp_dpcd_read_wake()

Since we've fixed up drm_dp_dpcd_read() to allow for retries when things
timeout, there's no use for having this function anymore. Good riddens.

Signed-off-by: Lyude <cpaul@redhat.com>
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1460559513-32280-5-git-send-email-cpaul@redhat.com