drm: panel: simple: Drop drive/sample bus flags for LVDS panels

The DRM bus flags reporting on which clock edge the pixel data and sync
signals are sampled or driven don't make sense for LVDS panels, as the
bus then uses sub-clock timings to send data. Drop those flags and add a
warning in the probe function to make sure the mistake won't be
repeated.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200629233320.8774-4-laurent.pinchart+renesas@ideasonboard.com