usb: USB download gadget and functions config options coherent naming

This introduces a coherent scheme for naming USB download gadget and functions
config options. The download USB gadget config option is moved to
CONFIG_USB_GADGET_DOWNLOAD for better consistency with other gadgets and each
function's config option is moved to a CONFIG_USB_FUNCTION_ prefix.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Tested-by: Lukasz Majewski <l.majewski@samsung.com>

Test HW: Odroid_XU3 (Exynos5422), trats (Exynos4210)
diff --git a/drivers/usb/gadget/Makefile b/drivers/usb/gadget/Makefile
index 70bb550..46d7d94 100644
--- a/drivers/usb/gadget/Makefile
+++ b/drivers/usb/gadget/Makefile
@@ -15,10 +15,10 @@
 obj-$(CONFIG_USB_GADGET_S3C_UDC_OTG_PHY) += s3c_udc_otg_phy.o
 obj-$(CONFIG_USB_GADGET_FOTG210) += fotg210.o
 obj-$(CONFIG_CI_UDC)	+= ci_udc.o
-obj-$(CONFIG_THOR_FUNCTION) += f_thor.o
-obj-$(CONFIG_USBDOWNLOAD_GADGET) += g_dnl.o
-obj-$(CONFIG_DFU_FUNCTION) += f_dfu.o
-obj-$(CONFIG_USB_GADGET_MASS_STORAGE) += f_mass_storage.o
+obj-$(CONFIG_USB_GADGET_DOWNLOAD) += g_dnl.o
+obj-$(CONFIG_USB_FUNCTION_THOR) += f_thor.o
+obj-$(CONFIG_USB_FUNCTION_DFU) += f_dfu.o
+obj-$(CONFIG_USB_FUNCTION_MASS_STORAGE) += f_mass_storage.o
 obj-$(CONFIG_CMD_FASTBOOT) += f_fastboot.o
 endif
 ifdef CONFIG_USB_ETHER