drm/bridge: Convert ps8622 into a drm_bridge

drm/bridge: Convert ps8622 into a drm_bridge

Change ps8622 driver from an i2c driver to a drm_bridge. This allows us
to control the bridge with dpms, as well as more tightly control the
order of power on.

BUG=chrome-os-partner:17557
TEST=Builds

Change-Id: Ie98b5728ee99cad311c72122fdf781b40467c126
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/43941
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>