ANDROID: usb: gadget: configfs: fix compiler warning

Commit 7a160e2b ("ANDROID: usb: gadget: configfs: Add Uevent to
notify userspace") introduces android_setup and android_disconnect
as alternatives to configfs_composite_setup and
configfs_composite_disconnect in case CONFIG_USB_CONFIGFS_UEVENT is set.
In case this config is set and in the presence of commit 1a1c851b
("usb: gadget: configfs: fix concurrent issue between composite APIs"),
the configfs_* functions are unused and therefore compilers complain
about that, e.g.

common/drivers/usb/gadget/configfs.c:1486:12: warning: unused function 'configfs_composite_setup' [-Wunused-function]

Fix that by conditionally compiling these functions.

Bug: 144674477
Fixes: 7a160e2b ("ANDROID: usb: gadget: configfs: Add Uevent to notify userspace")
Fixes: 1a1c851b ("usb: gadget: configfs: fix concurrent issue between composite APIs")
Change-Id: Idb6bb726d676d0d03b920375fd48fba41b60bb2d
Cc: Badhri Jagan Sridharan <Badhri@google.com>
Signed-off-by: Matthias Maennich <maennich@google.com>