OMAPDSS: DSI: Add FEAT_DSI_PLL_SELFREQDCO

Add FEAT_DSI_PLL_SELFREQDCO. OMAP5's DSI PLL has a new configuration
option that needs to be programmed depending on the PLL's output clock
frequency.

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