avr32: convert makefiles to Kbuild style

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Andreas Bießmann <andreas.devel@googlemail.com>
diff --git a/board/in-circuit/grasshopper/Makefile b/board/in-circuit/grasshopper/Makefile
index 1930e89..0457635 100644
--- a/board/in-circuit/grasshopper/Makefile
+++ b/board/in-circuit/grasshopper/Makefile
@@ -7,23 +7,4 @@
 #
 # SPDX-License-Identifier:	GPL-2.0+
 
-include $(TOPDIR)/config.mk
-
-LIB     := $(obj)lib$(BOARD).o
-
-COBJS-y += $(BOARD).o
-
-SRCS    := $(COBJS-y:.o=.c)
-OBJS    := $(addprefix $(obj),$(COBJS-y))
-
-$(LIB): $(obj).depend $(OBJS)
-	$(call cmd_link_o_target, $(OBJS))
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-#########################################################################
+obj-y += grasshopper.o