powerpc: Make sure that we alays include CONFIG_BINFMT_ELF

Our kernel is not much good without BINFMT_ELF and this fixes a build
warning on 64 bit allnoconfig builds:

warning: (COMPAT) selects COMPAT_BINFMT_ELF which has unmet direct dependencies (COMPAT && BINFMT_ELF)
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/Kconfig

@@ -90,6 +90,7 @@ config GENERIC_GPIO
 config PPC
 	bool
 	default y
+	select BINFMT_ELF
 	select OF
 	select OF_EARLY_FLATTREE
 	select HAVE_FTRACE_MCOUNT_RECORD