drm/radeon/kms: deal with connectors sourced to the same encoder

drm/radeon/kms: deal with connectors sourced to the same encoder

Some systems have multiple connectors connected to the same encoder;
e.g., DVI and HDMI connected to the same encoder with the same ddc
line. Since we expose connectors as xrandr outputs, randr treats them
separately which results in it trying to source the same encoder to
different crtcs. If we have an HDMI and DVI-D port on the same encoder,
pick the one to be considered connected based on the edid (HDMI if edid
indicates HDMI, DVI otherwise).

Should fix fdo bug 25150

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>