drm/bridge: synopsys: dw-hdmi: allow ycbcr420 modes for >= 0x200a

Now the DW-HDMI Controller supports the HDMI2.0 modes, enable support
for these modes in the connector if the platform supports them.
We limit these modes to DW-HDMI IP version >= 0x200a which
are designed to support HDMI2.0 display modes.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jernej Škrabec <jernej.skrabec@siol.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20200304104052.17196-6-narmstrong@baylibre.com