snd_uaudio: provide information about the device name and attached driver

Unlike the other sound drivers, snd_uaudio(4) doesn't provide
information about the device's description and the driver it's attached
to. A side-effect of this is that applications such as mixer(8), that
fetch these strings through the OSS API's SNDCTL_CARDINFO ioctl will
show a USB audio device as:

pcm0:mixer: <USB Audio> at ? kld snd_uaudio

This patch replaces the generic "USB Audio" description with the
device's actual manufacturer and product strings, and the "at ?" string
with the driver it's attached to:

pcm0:mixer: <Focusrite Scarlett Solo USB> at uaudio0 kld snd_uaudio

Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Reviewed by: markj, emaste
Differential Revision: https://reviews.freebsd.org/D43347