ALSA: usb-audio: Introduce USB SND platform op callbacks

Allow for different platforms to be notified on USB SND connect/disconnect
sequences.  This allows for platform USB SND modules to properly initialize
and populate internal structures with references to the USB SND chip
device.

Tested-by: Puma Hsu <pumahsu@google.com>
Tested-by: Daehwan Jung <dh10.jung@samsung.com>
Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250409194804.3773260-13-quic_wcheng@quicinc.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>