imx: nitrogen6x: mx6qsabrelite: Add support for DVI monitors

imx: nitrogen6x: mx6qsabrelite: Add support for DVI monitors

A little background is probably appropriate for this patch.

Since "the beginning" of usage of the SABRE Lite and Nitrogen6x
boards, DVI detection has been somewhat broken.

Some (most) DVI monitors don't produce the "HPD" bit in
the PHY_STAT0 register, but do show proper toggling of the
RX_SENSE0..3 bits.

Creating a new the bit-mask to include all five bits and
modifying the 'hdmidet' command and internal detection
routines allows these monitors to function properly in U-Boot.

A related patch to our kernels allows things to work under
Linux:
        https://github.com/boundarydevices/linux-imx6/commit/7d8752905c118af9063738a533227de0b2f6ecd4

Signed-off-by: Robert Winkler <robert.winkler@boundarydevices.com>
Acked-by: Stefano Babic <sbabic@denx.de>