[POWERPC] Fix bootwrapper builds with older gcc versions

GCC versions before 3.4 did not support the -mcpu=440 option.  Use
-mcpu=405 for the 4xx specific bootwrapper files, as that has been
around for much longer.
Signed-off-by: NJosh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

arch/powerpc/boot/Makefile

@@ -35,10 +35,10 @@ endif
 
 BOOTCFLAGS	+= -I$(obj) -I$(srctree)/$(obj) -I$(srctree)/$(src)/libfdt
 
-$(obj)/4xx.o: BOOTCFLAGS += -mcpu=440
-$(obj)/ebony.o: BOOTCFLAGS += -mcpu=440
-$(obj)/cuboot-taishan.o: BOOTCFLAGS += -mcpu=440
-$(obj)/cuboot-katmai.o: BOOTCFLAGS += -mcpu=440
+$(obj)/4xx.o: BOOTCFLAGS += -mcpu=405
+$(obj)/ebony.o: BOOTCFLAGS += -mcpu=405
+$(obj)/cuboot-taishan.o: BOOTCFLAGS += -mcpu=405
+$(obj)/cuboot-katmai.o: BOOTCFLAGS += -mcpu=405
 $(obj)/treeboot-walnut.o: BOOTCFLAGS += -mcpu=405