Architecture neutral code may need to call low-level io accessors,
or use spinlocks. Create a generic io.h to ensure those accessors
are defined, and a generic spinlock.h that complains when included,
as we can't write a generic spinlock. These files can be overridden
or extended by architecture specific versions placed in
lib/$ARCH/asm/.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
---
v5: added a trivial ioremap function [Christoffer Dall]
v4: introduce lib/asm symlink to get rid of #ifdef __arm__,
    add spinlock.h too
v3: wrt to io.h (was libio.[ch]) only
    - get rid of CONFIG_64BIT, replace with asserts
    - get rid of {read,write}_len() [libio.c]
    - fix bad *64_to_cpu macros