video: display_timing: Add flags to select the edge when the sync is driven

The sync can be - and for some panels it must be - driven on different edge
then the data.

Signed-off-by: Peter Ujfalusi <[e-mail]>
CC: Rob Herring <[e-mail]>
CC: Mark Rutland <[e-mail]>
CC: [e-mail]
Signed-off-by: Tomi Valkeinen <[e-mail]>

include/video/display_timing.h

···
 	DISPLAY_FLAGS_INTERLACED	= BIT(8),
 	DISPLAY_FLAGS_DOUBLESCAN	= BIT(9),
 	DISPLAY_FLAGS_DOUBLECLK		= BIT(10),
+	/* drive sync on pos. edge */
+	DISPLAY_FLAGS_SYNC_POSEDGE	= BIT(11),
+	/* drive sync on neg. edge */
+	DISPLAY_FLAGS_SYNC_NEGEDGE	= BIT(12),
 };
 
 /*