drivers: usb: convert makefiles to Kbuild style

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/drivers/usb/eth/Makefile b/drivers/usb/eth/Makefile
index 04a8b58..03f5474 100644
--- a/drivers/usb/eth/Makefile
+++ b/drivers/usb/eth/Makefile
@@ -3,31 +3,9 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
-
-LIB	:= $(obj)libusb_eth.o
-
 # new USB host ethernet layer dependencies
-COBJS-$(CONFIG_USB_HOST_ETHER) += usb_ether.o
+obj-$(CONFIG_USB_HOST_ETHER) += usb_ether.o
 ifdef CONFIG_USB_ETHER_ASIX
-COBJS-y += asix.o
+obj-y += asix.o
 endif
-COBJS-$(CONFIG_USB_ETHER_SMSC95XX) += smsc95xx.o
-
-COBJS	:= $(COBJS-y)
-SRCS	:= $(COBJS:.o=.c)
-OBJS	:= $(addprefix $(obj),$(COBJS))
-
-all:	$(LIB)
-
-$(LIB):	$(obj).depend $(OBJS)
-	$(call cmd_link_o_target, $(OBJS))
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-#########################################################################
+obj-$(CONFIG_USB_ETHER_SMSC95XX) += smsc95xx.o