drm/sun4i: lvds: Invert the LVDS polarity

The LVDS controller can invert the polarity / lanes of the LVDS output.
The default polarity causes some issues on some panels.

However, U-Boot has always used the opposite polarity without any reported
issue, and the only currently supported LVDS panel in-tree (the TBS A711)
seems to be able to work with both settings.

Let's just use the same polarity than U-Boot to be more consistent and
hopefully support all the panels.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Cc: Ondrej Jirman <megous@megous.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200704133803.37330-1-maxime@cerno.tech