drivers: convert makefiles to Kbuild style

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/drivers/bootcount/Makefile b/drivers/bootcount/Makefile
index 2b517b6..012acef 100644
--- a/drivers/bootcount/Makefile
+++ b/drivers/bootcount/Makefile
@@ -2,28 +2,8 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
-
-LIB 	:= $(obj)libbootcount.o
-
-COBJS-y				+= bootcount.o
-COBJS-$(CONFIG_AT91SAM9XE)	+= bootcount_at91.o
-COBJS-$(CONFIG_BLACKFIN)	+= bootcount_blackfin.o
-COBJS-$(CONFIG_SOC_DA8XX)	+= bootcount_davinci.o
-COBJS-$(CONFIG_BOOTCOUNT_RAM)	+= bootcount_ram.o
-
-COBJS	:= $(COBJS-y)
-SRCS 	:= $(COBJS:.o=.c)
-OBJS 	:= $(addprefix $(obj),$(COBJS))
-
-$(LIB):	$(obj).depend $(OBJS)
-	$(call cmd_link_o_target, $(OBJS))
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-########################################################################
+obj-y				+= bootcount.o
+obj-$(CONFIG_AT91SAM9XE)	+= bootcount_at91.o
+obj-$(CONFIG_BLACKFIN)		+= bootcount_blackfin.o
+obj-$(CONFIG_SOC_DA8XX)		+= bootcount_davinci.o
+obj-$(CONFIG_BOOTCOUNT_RAM)	+= bootcount_ram.o