powerpc: allyesconfig should not select CONFIG_CPU_LITTLE_ENDIAN

Stephen reported a failure in an allyesconfig build.
CONFIG_CPU_LITTLE_ENDIAN=y gets set but his toolchain is not
new enough to support little endian. We really want to
default to a big endian build; Ben suggested using a choice
which defaults to CPU_BIG_ENDIAN.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/Kconfig.cputype

@@ -404,13 +404,27 @@ config PPC_DOORBELL
 
 endmenu
 
-config CPU_LITTLE_ENDIAN
-	bool "Build little endian kernel"
-	default n
+choice
+	prompt "Endianness selection"
+	default CPU_BIG_ENDIAN
 	help
 	  This option selects whether a big endian or little endian kernel will
 	  be built.
 
+config CPU_BIG_ENDIAN
+	bool "Build big endian kernel"
+	help
+	  Build a big endian kernel.
+
+	  If unsure, select this option.
+
+config CPU_LITTLE_ENDIAN
+	bool "Build little endian kernel"
+	help
+	  Build a little endian kernel.
+
 	  Note that if cross compiling a little endian kernel,
 	  CROSS_COMPILE must point to a toolchain capable of targeting
 	  little endian powerpc.
+
+endchoice