After some more review comments from Roland, Andrew and Chris Hellwig,
here is a reworked set of 32-bit MMIO copy patches.

These use CONFIG_RAW_MEMCPY_IO to determine whether an arch should use
the generic __raw_memcpy_toio32 routine or its own specialised version.
We provide a specialised implementation for x86_64.

These patches should apply cleanly against current -git, and have been
tested on i386 and x86_64.

The patch series is as follows:

raw_memcpy_io.patch
  Introduce the generic MMIO 32-bit copy routine.

x86_64-memcpy32.patch
  Add memcpy32 routine to x86_64.

arch-specific-raw_memcpy_io.patch
  Get each arch to use generic memcpy_io code, except x86_64, which
  uses memcpy32.

Signed-off-by: Bryan O'Sullivan <bos@pathscale.com>