drm/omap: Move bus flag hack to encoder implementation

The bus flags stored in omap_dss_device instances are used to fixup the
video mode before setting it, to honour constraints that can't be
expressed through drm_display_mode. The fixup occurs in the CRTC mode
set operation and the resulting video mode is stored internally in the
CRTC. It is then used next by omap_encoder_enable() to apply mode fixups
for the omap_dss_device instances in omap_encoder_update().

Move the hack to the omap_encoder_update() function right before
applying the omap_dss_device fixups, in order to group all fixups
together.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>