powerpc: Move defconfig over and remove remaining arch/ppc64 files

make defconfig will now use arch/powerpc/configs/ppc64_defconfig
if running on a ppc64 system.  I need to add an
arch/powerpc/configs/ppc_defconfig sometime.

Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/Makefile

@@ -33,6 +33,8 @@ endif
 
 export CROSS32CC CROSS32AS CROSS32LD CROSS32OBJCOPY
 
+KBUILD_DEFCONFIG := $(shell uname -m)_defconfig
+
 ifeq ($(CONFIG_PPC64),y)
 OLDARCH	:= ppc64
 SZ	:= 64
@@ -111,9 +113,6 @@ cpu-as-$(CONFIG_E200)		+= -Wa,-me200
 AFLAGS += $(cpu-as-y)
 CFLAGS += $(cpu-as-y)
 
-# Default to the common case.
-KBUILD_DEFCONFIG := common_defconfig
-
 head-y				:= arch/powerpc/kernel/head_32.o
 head-$(CONFIG_PPC64)		:= arch/powerpc/kernel/head_64.o
 head-$(CONFIG_8xx)		:= arch/powerpc/kernel/head_8xx.o