CHROMIUM: exynos: dts: allow to switch off eDP bridge regulator

CHROMIUM: exynos: dts: allow to switch off eDP bridge regulator

We want to control the 1.2v regulator going to the eDP bridge from the
Parade driver.
In order to do this, we don't want to force it on all the time.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
BUG=chrome-os-partner:17866
TEST=on Spring, suspend with regulator traces and see the vdd_bridge
regulator going off.

Change-Id: I280844b3225cfa0f817a04190ca24779d26fa999
Reviewed-on: https://gerrit.chromium.org/gerrit/43532
Reviewed-by: Todd Broch <tbroch@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>