hcu4, hcu5: fix out of tree building

Out of tree building of the Netstal hcu4 and hcu5 boards failed like
that:

Assembler messages:
Fatal error: can't create /work/wd/tmp-ppc/board/netstal/hcu4/../common/fixed_sdram.o: No such file or directory
Assembler messages:
Fatal error: can't create /work/wd/tmp-ppc/board/netstal/hcu4/../common/nm_bsp.o: No such file or directory
make[1]: *** [/work/wd/tmp-ppc/board/netstal/hcu4/../common/fixed_sdram.o] Error 2

Adapt (and simplify) the respective Makefiles.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Niklaus Giger <niklaus.giger@netstal.com>
diff --git a/board/netstal/hcu5/Makefile b/board/netstal/hcu5/Makefile
index 4456771..d037552 100644
--- a/board/netstal/hcu5/Makefile
+++ b/board/netstal/hcu5/Makefile
@@ -19,22 +19,23 @@
 #
 
 include $(TOPDIR)/config.mk
+ifneq ($(OBJTREE),$(SRCTREE))
+$(shell mkdir -p $(obj)../common)
+endif
 
 LIB	= $(obj)lib$(BOARD).a
 
-
-# NOBJS : Netstal common objects
-NOBJS	= nm_bsp.o
-COBJS	= $(BOARD).o sdram.o
+COBJS	= $(BOARD).o \
+	sdram.o \
+	../common/nm_bsp.o
 SOBJS	= init.o
 
-SRCS	:= $(SOBJS:.o=.S) $(COBJS:.o=.c) $(addprefix ../common/,$(NOBJS:.o=.c))
+SRCS	:= $(SOBJS:.o=.S) $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(COBJS))
-NOBJS	:= $(addprefix $(obj)../common/,$(NOBJS))
 SOBJS	:= $(addprefix $(obj),$(SOBJS))
 
-$(LIB):	$(OBJS) $(SOBJS) $(NOBJS)
-	$(AR) $(ARFLAGS) $@ $(OBJS) $(SOBJS) $(NOBJS)
+$(LIB):	$(OBJS) $(SOBJS)
+	$(AR) $(ARFLAGS) $@ $^
 
 clean:
 	rm -f $(SOBJS) $(OBJS)