drm/bridge: anx7625: disable regulators when power off

When suspending the driver, anx7625_power_standby() will be called to
turn off reset-gpios and enable-gpios. However, power supplies are not
disabled. To save power, the driver can get the power supply regulators
and turn off them in anx7625_power_standby().

Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Reviewed-by: Xin Ji <xji@analogixsemi.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210401053202.159302-2-hsinyi@chromium.org