Previously in picking CRTC -> encoder -> connecting routing, we went for
the first triplet we found which claimed to work.

Preserving the existing routing means that startup will be faster: on a
multi-head system, changing the routing implies disabling both CRTCs,
then re-enabling them with a new configuration, which may involve
retraining links etc.

Furthermore, the existing routing may be set for a reason; each
CRTC/encoder is not necessarily as capable as the other, so the routing
may be configured to stay within such device limits.

Try where possible to respect the routing we pick up, rather than
blithely configuring our own.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>