write{b,w,l,q}_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 sparc, in the
same vein as the dummy definitions for the relaxed read accessors. The
existing relaxed read{b,w,l} accessors are moved into asm/io.h, since
they are identical between 32-bit and 64-bit machines.
Acked-by: N"David S. Miller" <davem@davemloft.net>
Acked-by: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>