config: set ARCH if powerpc64 is selected in the configuration

Signed-off-by: Florian Larysch <[email protected]>

target/Config.in

@@ -199,6 +199,7 @@ config ARCH
 	default "mips64"    if mips64
 	default "mips64el"  if mips64el
 	default "powerpc"   if powerpc
+	default "powerpc64" if powerpc64
 	default "sh3"       if sh3
 	default "sh3eb"     if sh3eb
 	default "sh4"       if sh4