drmmode: fetch each connector's DPMS property id just once

Fetch each connector's "DPMS" property id just once, when creating its
xf86Output.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>

BUG=chromium:370411
TEST=sanity check ui w/ suspend/resume, HDMI hotplug
TEST=DISPLAY=:0 xrandr --output HDMI-1 --off
  => External display turns off, then back on

Change-Id: I6da087ea7c1d63da193874264df4447a373939fc
Reviewed-on: https://chromium-review.googlesource.com/198390
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Tested-by: Daniel Kurtz <djkurtz@chromium.org>
1 file changed