s390: Stop using weak symbols for __iowrite64_copy()

s390: Stop using weak symbols for __iowrite64_copy()

Complete switching the __iowriteXX_copy() routines over to use #define and
arch provided inline/macro functions instead of weak symbols.

S390 has an implementation that simply calls another memcpy
function. Inline this so the callers don't have to do two jumps.

Link: https://lore.kernel.org/r/3-v3-1893cd8b9369+1925-mlx5_arm_wc_jgg@nvidia.com
Acked-by: Niklas Schnelle <schnelle@linux.ibm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>