usb: gadget: acm_ms: use function framework for ACM

This patch converts the acm_ms gadget to make use of the function
framework to request the ACM function.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig
index b61c72f..8dad2ce 100644
--- a/drivers/usb/gadget/Kconfig
+++ b/drivers/usb/gadget/Kconfig
@@ -844,6 +844,7 @@
 	depends on BLOCK
 	select USB_LIBCOMPOSITE
 	select USB_U_SERIAL
+	select USB_F_ACM
 	help
 	  This driver provides two functions in one configuration:
 	  a mass storage, and a CDC ACM (serial port) link.