OMAP: DSS2: DISPC: improve dispc_mgr_enable_digit_out()

dispc_mgr_enable_digit_out() didn't handle HDMI case very well.

Improve the function to use FRAMEDONETV interrupt to see when HDMI has
been disabled.

Cc: Mythri P K <mythripk@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>