arm: mx6: cm-fx6: map HDMI to IPU1 DI0 explicitly

U-Boot does not explicitly assign the display to an IPU interface. Instead, it
relies on the power-on default of DI0.

Since the kernel reassigns HDMI display to DI1, after a warm reset the HDMI
display no longer works in U-Boot.

Fix this by explicitly assigning HDMI to IPU1 DI0 in U-Boot.

Cc: Stefano Babic <sbabic@denx.de>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>