OMAPDSS: DISPC: explicit handling for sync and de levels

When configuring the lcd timings, instead of writing enum values
directly to the HW, use switch-case to get the value to be programmed.

This is safer and also allows us to change the enum values.

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

diff --cc drivers/video/fbdev/omap2/dss/dispc.c
Simple merge