OMAP: DSS2: Adding dss_features for independent core clk divider

In OMAP3xxx DISPC_DIVISOR register has a logical clock divisor (lcd_div)
field. The lcd_div is common, for deciding the DISPC core functional clock
frequency, and the final pixel clock frequency for LCD display.

In OMAP4, there are 2 LCD channels, hence two divisor registers, DISPC_DIVISOR1
and DISPC_DIVISOR2. Also, there is a third register DISPC_DIVISOR.

The DISPC_DIVISOR in OMAP4 is used to configure lcd_div exclusively for core
functional clock configuration. For pixel clock configuration of primary and
secondary LCDs, lcd_div of DISPC_DIVISOR1 and DISPC_DIVISOR2 are used
respectively

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