drm/rockchip: dw_hdmi: add regulator support

The RK3568 has HDMI_TX_AVDD0V9 and HDMI_TX_AVDD_1V8 supply inputs needed
for the HDMI port. add support for these to the driver for boards which
have them supplied by switchable regulators.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Tested-by: Michael Riesch <michael.riesch@wolfvision.net>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220422072841.2206452-10-s.hauer@pengutronix.de