compositor-drm: rename outputs to follow kernel style

compositor-drm: rename outputs to follow kernel style

The problem with the old table of names is that it contains duplicates.
It is possible to end up with multiple outputs with the same name. In
that case you cannot write individual configurations for these outputs
in weston.ini, because they are matched by the name.

Change all names to follow the kernel naming scheme set in
drivers/gpu/drm/drm_crtc.c. The snprintf format now follows the kernel
style, too. Use the DRM_MODE_CONNECTOR_* macros rather than implicit
table ordering.

Completely new entries in the table are "Virtual" and "DSI".

There should not be any gaps in the macro values, but if there are, deal
with a NULL entry.

Also change "UNKNOWN" to "UNNAMED" so it's easier to distinguish from
"Unknown" by the kernel.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89361
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>
Tested-by: Drew DeVault <sir@cmpwn.com>