[POWERPC] Select proper defconfig for crosscompiles

The trick for finding the right defconfig is neat, but you forgot to
provide an i686_defconfig.  ;-)

More seriously, cross compiling the defconfig is often useful, e.g. for
testing the compilation of patches that touch multiple architectures,
and this patch therefore chooses g5_defconfig if $(CROSS_COMPILE) is
non-empty.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Olof Johansson <olof@lixom.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/Makefile

@@ -35,7 +35,11 @@ endif
 
 export CROSS32CC CROSS32AS CROSS32LD CROSS32AR CROSS32OBJCOPY
 
+ifeq ($(CROSS_COMPILE),)
 KBUILD_DEFCONFIG := $(shell uname -m)_defconfig
+else
+KBUILD_DEFCONFIG := ppc64_defconfig
+endif
 
 ifeq ($(CONFIG_PPC64),y)
 OLDARCH	:= ppc64