OMAPDSS: DSI: Add code to disable PHY DCC

OMAP5 DSI PHY has DCC (Duty Cycle Corrector) block, and by default DCC
is enabled and thus the PLL clock is divided by 2 to get the DSI DDR
clk. This divider has been 4 for all previous OMAPs, and changing it
needs some reorganization of the code. The DCC can be disabled, and in
that case the divider is back to the old 4.

This patch adds dss feature for the DCC, and adds code to always disable
the DCC.

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