OMAP: DSS2: Introduce omap_channel as an omap_dss_device parameter, add new overlay...

OMAP: DSS2: Introduce omap_channel as an omap_dss_device parameter, add new overlay manager.

A panel connects to one of the overlay managers of DSS through some interface block.
On OMAP4, specifying the type of the display is not sufficient to conclude which manager
the panel should be connected to.
Hence, a new member 'channel' is introduced in omap_dss_device structure to determine
which manager the panel uses. The dss_recheck_connections() called in dss_driver_probe()
uses this channel parameter to set the correct manager to the corresponding omap_dss_device.

The channel parameter is used only once to ensure the correct managers are set for each
panel. The parameter dssdev->manager->id will take care of ensuring that the panel and
then the interface driver configures the correct DISPC channel.

Also, add a new Overlay Manager in manager.c, make other changes needed for LCD2 channel.

Signed-off-by: Sumit Semwal <sumit.semwal@ti.com>
Signed-off-by: Mukund Mittal <mmittal@ti.com>
Signed-off-by: Samreen <samreen@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>