drm: bridge: dw_hdmi: fix preference of RGB modes over YUV420

drm: bridge: dw_hdmi: fix preference of RGB modes over YUV420

Cheap monitors sometimes advertise YUV modes they don't really have
(HDMI specification mandates YUV support so even monitors without actual
support will often wrongfully advertise it) which results in YUV matches
and user forum complaints of a red tint to light colour display areas in
common desktop environments.

Moving the default RGB fall-back before YUV selection results in RGB
mode matching in most cases, reducing complaints.

Fixes: 6c3c719936da ("drm/bridge: synopsys: dw-hdmi: add bus format negociation")
Signed-off-by: Guillaume BRUN <the.cheaterman@gmail.com>
Tested-by: Christian Hewitt <christianshewitt@gmail.com>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20221116143523.2126-1-the.cheaterman@gmail.com