board: powerpc: convert makefiles to Kbuild style

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Kim Phillips <kim.phillips@freescale.com>
Cc: York Sun <yorksun@freescale.com>
Cc: Stefan Roese <sr@denx.de>
diff --git a/board/freescale/p1_twr/Makefile b/board/freescale/p1_twr/Makefile
index 915b9bc..70afac4 100644
--- a/board/freescale/p1_twr/Makefile
+++ b/board/freescale/p1_twr/Makefile
@@ -3,33 +3,7 @@
 #
 # SPDX-License-Identifier:	GPL-2.0+
 
-include $(TOPDIR)/config.mk
-
-LIB    = $(obj)lib$(BOARD).o
-
-COBJS-y        += $(BOARD).o
-COBJS-y        += ddr.o
-COBJS-y        += law.o
-COBJS-y        += tlb.o
-
-SRCS   := $(SOBJS:.o=.S) $(COBJS-y:.o=.c)
-OBJS   := $(addprefix $(obj),$(COBJS-y))
-SOBJS  := $(addprefix $(obj),$(SOBJS))
-
-$(LIB):	$(obj).depend $(OBJS) $(SOBJS)
-	$(call cmd_link_o_target, $(OBJS))
-
-clean:
-	rm -f $(OBJS) $(SOBJS)
-
-distclean:	clean
-	rm -f $(LIB) core *.bak .depend
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-#########################################################################
+obj-y        += p1_twr.o
+obj-y        += ddr.o
+obj-y        += law.o
+obj-y        += tlb.o