OMAPDSS: DPI: Store dpi_data pointer in the DT port's data

DPI and SDI ports are backed by only one parent DSS device. We don't have a
corresponding platform_device for ports under DSS. In order to support multiple
instances of DPI, we need to pass the driver data pointer through the DPI port's
private data ('data' member in device_node struct).

dpi_init_output/dpi_uninit_output are untouched and only used for non-DT case,
these are called when the DPI platform device probed/removed. These funcs will
be removed when non-DT mode is removed.

dpi_init_output_port/dpi_uninit_output_port are created and used for the DT
path, called when DSS inits/uninits it's ports. These new functions retrieve
the dpi_data pointer from 'port->data', and not from the platform device's
data(pdev->dev) like in the non-DT path.

We add some code in dss_uninit_ports() to pass a pointer to the DPI port in
dpi_uninit_port().

Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>