usb: gadget: f_uac2: Support multiple sampling rates

A list of sampling rates can be specified via configfs. All enabled
sampling rates are sent to the USB host on request. When the host
selects a sampling rate, the internal active rate (stored in
struct f_uac2) is updated.

The gadget no longer supports only one frequency. Therefore USB strings
corresponding to the clock sources are renamed from specific Hz value to
general names Input clock/Output clock.

Config strings with single value stay compatible with the previous
version.

Multiple samplerates passed as configuration arrays to g_audio module
when built for f_uac2.

Signed-off-by: Julian Scheel <julian@jusst.de>
Signed-off-by: Pavel Hofman <pavel.hofman@ivitera.com>
Link: https://lore.kernel.org/r/20220121155308.48794-6-pavel.hofman@ivitera.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>