mx6cuboxi: Allow HDMI and USB keyboard to be stdout/stdin

mx6cuboxi: Allow HDMI and USB keyboard to be stdout/stdin

There are users of Cuboxi and Hummingboard that use these boards without
connecting them to a USB/serial adapter.

Allow such usage by allowing the HDMI port to act as stdout and USB keyboard
as stdin.

The serial console still also works as stdin/stdout.

Signed-off-by: Rabeeh Khoury <rabeeh@solid-run.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Tested-by: Vagrant Cascadian <vagrant@aikidev.net>