drm/radeon/kms: add support for clock/data path routers

drm/radeon/kms: add support for clock/data path routers

This is a follow on to:
ed84bd61be0576e2b069ff769eca598775f1d899
(drm/radeon/kms: add support for router objects)

That patch added support for systems that use a mux to control
the ddc line routing between the connectors.  This patch adds
support for systems that use a mux to control the encoder
clock and data path routing to the connectors.

Should fix:
https://bugs.freedesktop.org/show_bug.cgi?id=31339

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