asm-generic: add generic atomic.h and io.h

atomic.h and io.h are based on the mn10300 architecture,
which is already pretty generic and can be used by
other architectures that do not have hardware support
for atomic operations or out-of-order I/O access.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

diff --cc include/asm-generic/atomic.h
Simple merge

diff --cc include/asm-generic/io.h
Simple merge