OMAPDSS: DSI: use new clock calculation code

Use the new clock calculation code in the DSI driver.

The new code does not need DSI video mode parameters from the panel
driver, like the old code does. Instead the new code is given the normal
video timings, and a few DSI parameters, which are used to create DSI
video timings.

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