OMAPDSS: add setup for WB capture mode in dispc_wb_setup()

dispc_wb_setup() handles configuration only for mem-to-mem case. This
patch adds the necessary configuration to handle also display capture
mode.

We need to set CAPTUREMODE to 0 (continuous capture), and WBDELAYCOUNT
according to the vertical timings of the display, so that the WB FIFO
has time to flush before the next frame starts.

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