drm/panel: lvds: Use bus_flags from DT panel-timing property

This driver currently rewrites bus_flags based solely on the value of
DT property 'data-mirror' and ignores bus_flags which might have been
set in DT panel-timing node. Specificaly, the 'de-active' DT property
sets DRM_BUS_FLAG_DE_ bus_flags.

Since of_get_drm_panel_display_mode() conveniently parses the bus_flags
out of DT panel-timing property, just ORR them with bus_flags inferred
from 'data-mirror' DT property and use the result as panel bus_flags.

This fixes handling of panels with 'panel-timing { de-active = <1>; };'.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dmitry Osipenko <digetx@gmail.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Robert Foss <robert.foss@linaro.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
To: dri-devel@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20220401162154.295152-2-marex@denx.de