m32r: io: implement dummy relaxed accessor macros for writes

write{b,w,l}_relaxed are implemented by some architectures in order to
permit memory-mapped I/O accesses with weaker barrier semantics than the
non-relaxed variants.

This patch adds dummy macros for the write accessors to m32r, in the
same vein as the dummy definitions for the relaxed read accessors.

Cc: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/m32r/include/asm/io.h

@@ -161,6 +161,9 @@ static inline void _writel(unsigned long l, unsigned long addr)
 #define __raw_writeb writeb
 #define __raw_writew writew
 #define __raw_writel writel
+#define writeb_relaxed writeb
+#define writew_relaxed writew
+#define writel_relaxed writel
 
 #define ioread8 read
 #define ioread16 readw