common: Make sure arch-specific map_sysmem() is defined

In the case where the arch defines a custom map_sysmem(), make sure that
including just mapmem.h is sufficient to have these functions as they
are when the arch does not override it.

Also split the non-arch specific functions out of common.h

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/mapmem.h b/include/mapmem.h
new file mode 100644
index 0000000..42ef3e8
--- /dev/null
+++ b/include/mapmem.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2015 National Instruments
+ *
+ * (C) Copyright 2015
+ * Joe Hershberger <joe.hershberger@ni.com>
+ *
+ * SPDX-License-Identifier:    GPL-2.0
+ */
+
+#ifndef __MAPMEM_H
+#define __MAPMEM_H
+
+/* Define a null map_sysmem() if the architecture doesn't use it */
+# ifdef CONFIG_ARCH_MAP_SYSMEM
+#include <asm/io.h>
+# else
+static inline void *map_sysmem(phys_addr_t paddr, unsigned long len)
+{
+	return (void *)(uintptr_t)paddr;
+}
+
+static inline void unmap_sysmem(const void *vaddr)
+{
+}
+
+static inline phys_addr_t map_to_sysmem(const void *ptr)
+{
+	return (phys_addr_t)(uintptr_t)ptr;
+}
+# endif
+
+#endif /* __MAPMEM_H */