[POWERPC] Create and use CONFIG_WORD_SIZE

Linus made this suggestion for the x86 merge and this starts the process
for powerpc.  We assume that CONFIG_PPC64 implies CONFIG_PPC_MERGE and
CONFIG_PPC_STD_MMU_32 implies CONFIG_PPC_STD_MMU.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 26126d2..45e86c7 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -14,6 +14,11 @@
 	bool
 	default y if PPC64
 
+config WORD_SIZE
+	int
+	default 64 if PPC64
+	default 32 if !PPC64
+
 config PPC_MERGE
 	def_bool y