Makefile: convert makefiles to Kbuild style and delete grep switch

We have converted all makefiles needed to build $(LIBS).

Until this commit we used to grep switch so that U-Boot style
and Kbuild style makefiles coexist.
But we do not need any more.

Goint forward, use always Kbuild style Makefile when adding
a new Makefile

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/board/xilinx/ppc405-generic/Makefile b/board/xilinx/ppc405-generic/Makefile
index cc161ae..1562f17 100644
--- a/board/xilinx/ppc405-generic/Makefile
+++ b/board/xilinx/ppc405-generic/Makefile
@@ -9,27 +9,8 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
 ifneq ($(OBJTREE),$(SRCTREE))
 $(shell mkdir -p $(obj)../../xilinx/ppc405-generic)
 endif
 
-LIB	= $(obj)lib$(BOARD).o
-
-COBJS	+= ../../xilinx/ppc405-generic/xilinx_ppc405_generic.o
-
-SRCS	:= $(SOBJS:.o=.S) $(COBJS:.o=.c)
-OBJS	:= $(addprefix $(obj),$(COBJS))
-SOBJS	:= $(addprefix $(obj),$(SOBJS))
-
-$(LIB):	$(obj).depend $(OBJS) $(SOBJS)
-	$(call cmd_link_o_target, $(OBJS))
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-#########################################################################
+obj-y	+= ../../xilinx/ppc405-generic/xilinx_ppc405_generic.o