dt-bindings: power: imx8mp: add defines for HDMI blk-ctrl domains

This adds the defines for the power domains provided by the HDMI
blk-ctrl on the i.MX8MP.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>