OMAP: DSS2: DSI: Fix DSI PLL power bug

OMAP3630 has a HW bug causing DSI PLL power command POWER_ON_DIV (0x3)
to not work properly. The bug prevents us from enabling DSI PLL power
only to HS divider block.

This patch adds a dss feature for the bug and converts POWER_ON_DIV
requests to POWER_ON_ALL (0x2).

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