dt-bindings: drm/panel: boe-tv101wum-nl6: Support enabling a 3.3V rail

The auo,b101uan08.3 panel (already supported by this driver) has
a 3.3V rail that needs to be turned on. For previous users of
this panel this voltage was directly output by pmic. On a new
user (the not-yet-upstream sc7180-trogdor-mrbland board) we need
to turn the 3.3V rail on.

Signed-off-by: yangcong <yangcong5@huaqin.corp-partner.google.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210914032252.3770756-3-yangcong5@huaqin.corp-partner.google.com