board: ti: convert makefiles to Kbuild style

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Tom Rini <trini@ti.com>
diff --git a/board/ti/am43xx/Makefile b/board/ti/am43xx/Makefile
index 4a1bb7c..cb5fe88 100644
--- a/board/ti/am43xx/Makefile
+++ b/board/ti/am43xx/Makefile
@@ -6,33 +6,8 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
-
-LIB	= $(obj)lib$(BOARD).o
-
 ifdef CONFIG_SPL_BUILD
-COBJS	:= mux.o
+obj-y	:= mux.o
 endif
 
-COBJS	+= board.o
-SRCS	:= $(COBJS:.o=.c)
-OBJS	:= $(addprefix $(obj),$(COBJS))
-SOBJS	:= $(addprefix $(obj),$(SOBJS))
-
-$(LIB):	$(obj).depend $(OBJS) $(SOBJS)
-	$(call cmd_link_o_target, $(OBJS) $(SOBJS))
-
-clean:
-	rm -f $(SOBJS) $(OBJS)
-
-distclean:	clean
-	rm -f $(LIB) core *.bak $(obj).depend
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-#########################################################################
+obj-y	+= board.o