alsa-ucm: fix persistent port names with alsa-lib >= 1.2.5

alsa-ucm: fix persistent port names with alsa-lib >= 1.2.5

Alsa UCM device string can contain private configuration prefix required to make
correct device open call. Private prefix is dynamically generated by UCM manager
depending on internal state. Since pulseaudio sink/source port names currently
contain device string, these may change between runs breaking volume database
and module arguments referring to sink/source.

Fix this by skipping UCM private prefix available via `_alibpref` key while
creating UCM mapping name. Mapping object will still contain unmodified
device string for device open call.

See also https://github.com/alsa-project/alsa-ucm-conf/issues/104

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/598>