dt-bindings: display: sun4i-drm: Add R40 TV TCON description

TCON description is expanded with R40 TV TCON compatible. It is a bit
special, because it is connected to TCON TOP instead directly to mixer
and it needs special handling.

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180710203511.18454-7-jernej.skrabec@siol.net