OMAPDSS: SDI: Create a function to set timings

Create function omapdss_sdi_set_timings(). Configuring new timings is done the
same way as before, SDI is disabled, and re-enabled with the new timings in
dssdev. This just moves the code from the panel drivers to the SDI driver.

The panel drivers shouldn't be aware of how SDI manages to configure a new set
of timings. This should be taken care of by the SDI driver itself.

Signed-off-by: Archit Taneja <archit@ti.com>