Kconfig: gadget: Move CONFIG_USB_FUNCTION_MASS_STORAGE to Kconfig

This commit moves USB_FUNCTION_MASS_STORAGE config to Kconfig.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/configs/CHIP_pro_defconfig b/configs/CHIP_pro_defconfig
index 02e79b5..3b3a316 100644
--- a/configs/CHIP_pro_defconfig
+++ b/configs/CHIP_pro_defconfig
@@ -25,3 +25,4 @@
 CONFIG_USB_EHCI_HCD=y
 CONFIG_USB_MUSB_GADGET=y
 CONFIG_SYS_USB_EVENT_POLL_VIA_INT_QUEUE=y
+CONFIG_USB_FUNCTION_MASS_STORAGE=y