arm64: dts: freescale: imx8mm-phyboard: Add I2C4 pinmuxing

The I2C4 bus is exposed on the camera connector. Add and select the
corresponding pinmux entries and set the default frequency. The device
is left disabled, to be enabled from camera overlays.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Teresa Remmet <t.remmet@phytec.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>