compositor-drm: unify head status logging

Previously the log contained one line for EDID data and another line for
the head, and you just had to know they belong together. Make it more
obvious to read by putting both head and EDID info on the same line.

We no longer print EDID data every time it is parsed (on every hotplug
event), but only if it changes. I did take a shortcut here and use
weston_head::device_changed as the print condition which relies on the
compositor clearing it, but a failure to do so just means we print stuff
even if it didn't change.

Head info updates also print the head info and not just the EDID data.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Acked-by: Derek Foreman <derekf@osg.samsung.com>