MLK-17275-9: dts: imx8qxp-mek: Enable IT6263 and ADV7535

MLK-17275-9: dts: imx8qxp-mek: Enable IT6263 and ADV7535

Final step for the OF_DYNAMIC support: enable the LVDS and MIPI-DSI
to HDMI converter nodes by default in the main DTS file for each
platform.
This patch enables these nodes for i.MX8QXP MEK board.
Also, use adi,dsi-channel = <1> for ADV7535, since the panel can
only work on channel 0. By using channel 1 for ADV7535, we can have them
work simultaneously: one on DSI0 and the other on DSI1.

Signed-off-by: Robert Chiras <robert.chiras@nxp.com>