OMAPDSS: DSS: init dss ports cleanly

The init/uninit port functions are used to set up the DPI and SDI outputs under
the dss platform device. A 'reg' property is used to determine the port number
of the output. This tells us whether the port is DPI or SDI for OMAP34xx DSS
revision. For other DSS revisions, we only have DPI outputs under the dss
platform device.

For multiple DPI output instances(introduced in DRA7xx DSS), we will use the
the port number to specify which DPI output instance is being inited.

The current functions work fine if there is only one DPI output instance in
DSS. For multiple DPI instances, it would get complicated to figure out whether
port number was used to specify whether the output is SDI, or another DPI
instance.

We create a list of port types supported for each DSS rev, with the index of the
port in the list specifying the port number of the output for that DSS revision.
This allows us to have a more generic way to init/uninit ports within DSS, and
also support multiple DPI ports.

We make the uninit_port functions iterative since we will have multiple DPI
ports to uninit in the future.

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