ARM: dts: imx6-sabreauto: add video capture ports and endpoints

Defines the host v4l2-capture device node and the ADV7180 decoder
sensor. The host capture device is a child of ipu1. The ADV7180 is
connected to the host parallel-bus endpoint on CSI0.

On the sabreauto, two analog video inputs are routed to the ADV7180,
composite on Ain1, and composite on Ain3. Those inputs are defined
via inputs and input-names under the host endpoint node on CSI0.

Regulators and port expanders are defined which are required for the
ADV7180 (power pin is via port expander gpio on i2c3). The reset pin
to the port expander chip (MAX7310) is controlled by a gpio, so define
the reset-gpios property to control it.

The sabreauto uses a steering pin to select between the SDA signal on
i2c3 bus, and a data-in pin for an SPI NOR chip. Use i2cmux to control
this steering pin. Idle state of the i2cmux selects SPI NOR. This is not
a classic way to use i2cmux, since one side of the mux selects something
other than an i2c bus, but it works and is probably the cleanest
solution. Note that if one thread is attempting to access SPI NOR while
another thread is accessing i2c3, the SPI NOR access will fail since the
i2cmux has selected the SDA pin rather than SPI NOR data-in. This couldn't
be avoided in any case, the board is not designed to allow concurrent
i2c3 and SPI NOR functions (and the default device-tree does not enable
SPI NOR anyway).

Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>