intel-virtual-output: Iterate over remote outputs in the same order as listed

intel-virtual-output: Iterate over remote outputs in the same order as listed

If we walk the output lists in the same order as they are listed by
RandR, we are more likely to hit favourable priority sorting. E.g. the
user is likely to setup the outputs in the same order as listed, meaning
fewer CRTC transitions etc.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>