alpha: io: implement relaxed accessor macros for writes

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

This patch implements these write macros for Alpha, in the same vein as
the relaxed read macros, which are already implemented.
Acked-by: NRichard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NMatt Turner <mattst88@gmail.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/alpha/include/asm/io.h

@@ -504,6 +504,10 @@ extern inline void writeq(u64 b, volatile void __iomem *addr)
 #define readw_relaxed(addr)	__raw_readw(addr)
 #define readl_relaxed(addr)	__raw_readl(addr)
 #define readq_relaxed(addr)	__raw_readq(addr)
+#define writeb_relaxed(b, addr)	__raw_writeb(b, addr)
+#define writew_relaxed(b, addr)	__raw_writew(b, addr)
+#define writel_relaxed(b, addr)	__raw_writel(b, addr)
+#define writeq_relaxed(b, addr)	__raw_writeq(b, addr)
 
 #define mmiowb()