ppc/85xx: Simplify the top makefile for 36-bit config for P2020DS

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/Makefile b/Makefile
index 8672336..1e25669 100644
--- a/Makefile
+++ b/Makefile
@@ -2518,12 +2518,7 @@
 
 P2020DS_36BIT_config \
 P2020DS_config:		unconfig
-	@mkdir -p $(obj)include
-	@if [ "$(findstring _36BIT_,$@)" ] ; then \
-		echo "#define CONFIG_PHYS_64BIT" >>$(obj)include/config.h ; \
-		$(XECHO) "... enabling 36-bit physical addressing." ; \
-	fi
-	@$(MKCONFIG) -a P2020DS ppc mpc85xx p2020ds freescale
+	@$(MKCONFIG) -t $(@:_config=) P2020DS ppc mpc85xx p2020ds freescale
 
 P1011RDB_config:	unconfig
 	@mkdir -p $(obj)include