Introduce __iowrite64_copy.  It will be used by the Myri-10G Ethernet
driver to post requests to the NIC.  This driver will be submitted soon.

__iowrite64_copy copies to I/O memory in units of 64 bits when possible (on
64 bit architectures).  It reverts to __iowrite32_copy on 32 bit
architectures.

Signed-off-by: Brice Goglin <brice@myri.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>