arm64: dts: imx8mp: add HDMI power-domains

This adds the PGC and HDMI blk-ctrl nodes providing power control for
HDMI subsystem peripherals.

Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Tested-by: Marek Vasut <marex@denx.de>
Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Tested-by: Tommaso Merciai <tomm.merciai@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>