UPSTREAM: usb: gadget: f_uac2: allow changing interface name via configfs

This adds "function_name" configfs entry to change string value
of the iInterface field. This field will be shown in Windows' audio
settings panel, so being able to change it is useful. It will default
to "Source/Sink" just as before.

Signed-off-by: Yunhao Tian <t123yh.xyz@gmail.com>
Link: https://lore.kernel.org/r/20220122112446.1415547-2-t123yh.xyz@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Bug: 235196743
(cherry picked from commit 993a44fa)
Change-Id: I6061d841eee5b611f18280c901849d0c4b2a17d4
Signed-off-by: Luiz Matheus <luizmmat@motorola.com>