arm64: dts: imx8mp: Enable HDMI on i.MX8MP DHCOM PDK2 and PDK3

Enable HDMI output on i.MX8MP DHCOM PDK2 and PDK3. The I2C5 on PDK2 and
I2C mux port 1 on PDK3 respectively are used in regular I2C mode instead
of HDMI DDC mode to permit connection of other I2C devices on those buses.
The pinctrl_hdmi node is part of the SoM DTSI already.

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>