OMAP2, 3: DSS2: board files: replace platform_device_register with omap_display_init()

This patch updated board files to replace platform_device_register or
platform_add_devices of DSS with omap_display_init(). This moves away
registration of DSS from board files into a common place.

Reviewed-by: Kevin Hilman <khilman@ti.com>
Tested-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Sumit Semwal <sumit.semwal@ti.com>
Signed-off-by: Senthilvadivu Guruswamy <svadivu@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>