ppc: Enable generic board support

This enables generic board support so that ppc boards can define
CONFIG_SYS_GENERIC_BOARD.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/config.mk b/arch/powerpc/config.mk
index b706281..e32d2bf 100644
--- a/arch/powerpc/config.mk
+++ b/arch/powerpc/config.mk
@@ -29,6 +29,9 @@
 PLATFORM_CPPFLAGS += -DCONFIG_PPC -D__powerpc__
 PLATFORM_LDFLAGS  += -n
 
+# Support generic board on PPC
+__HAVE_ARCH_GENERIC_BOARD := y
+
 #
 # When cross-compiling on NetBSD, we have to define __PPC__ or else we
 # will pick up a va_list declaration that is incompatible with the