OMAPDSS: DISPC: Use a common function to set manager timings

Currently, a LCD manager's timings is set by dispc_mgr_set_lcd_timings() and TV
manager's timings is set by dispc_set_digit_size(). Use a common function called
dispc_mgr_set_timings() which sets timings for both type of managers.

We finally want the interface drivers to use an overlay manager function to
configure it's timings, having a common DISPC function would make things
cleaner.

For LCD managers, dispc_mgr_set_timings() sets LCD size and blanking values, for
TV manager, it sets only the TV size since blanking values don't exist for TV.

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