drm/panel: panel-simple: drop use of legacy drm_bus_flags

Replace all uses of the legacy drm_bus_flags with their relevant
_SAMPLE_ variant.
This is a 1:1 replacement, no effort was made to validate the actual
bus flags for the panels.

Note:
DRM_BUS_FLAG_PIXDATA_SAMPLE_POSEDGE = DRM_BUS_FLAG_PIXDATA_NEGEDGE
DRM_BUS_FLAG_PIXDATA_SAMPLE_NEGEDGE = DRM_BUS_FLAG_PIXDATA_POSEDGE

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200630180545.1132217-6-sam@ravnborg.org