drm/sun4i: tcon: add support for V3s TCON

Allwinner V3s SoC features a TCON without channel 1.

Add support for it.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>