[PATCH 0 of 3] Add memcpy_toio32, a 32-bit MMIO copy routine

[Bryan O'Sullivan]

Following some discussion with Matt, Andrew and Chris, here is a recast
of the 32-bit MMIO patch I posted the other day.  The routine is now
named memcpy_toio32, and is provided in generic and x86_64-optimised
forms.

I haven't added a memcpy_fromio32, or routines for other access sizes,
because our hardware doesn't need them.  If someone wants them for
reasons of symmetry, I can introduce them.

Signed-off-by: Bryan O'Sullivan <bos@xxxxxxxxxxxxx>