powerpc: Add linkage.h file

This permits us to use linux/linkage.h on PowerPC machines.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/include/asm/linkage.h b/arch/powerpc/include/asm/linkage.h
new file mode 100644
index 0000000..559b42e
--- /dev/null
+++ b/arch/powerpc/include/asm/linkage.h
@@ -0,0 +1,7 @@
+/*
+ * Copyright (c) 2014 Google, Inc
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+/* We don't need anything here at present */