drm/sun4i: tcon: Introduce LVDS setup routine setting

Different sunxi flavors require slightly different sequence for enabling
LVDS output. This allows to differentiate between them.

Signed-off-by: Andrey Lebedev <andrey@lebedev.lt>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20200219180858.4806-2-andrey.lebedev@gmail.com