OMAPDSS: DSI: remove DSI & DISPC clk divisors from dssdev

struct omap_dss_device contains DSS clock divisors. The idea is that the
board file can pass precalculated divisors to the display driver.
However, these divsors are no longer needed, as the omapdss driver can
calculate the divisors during runtime.

This patch removes the divisors from omap_dss_device, and their uses
from the dsi driver.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Archit Taneja <archit@ti.com>