powerpc: iomap.c: introduce io{read|write}64_{lo_hi|hi_lo}

These functions will be introduced into the generic iomap.c so they
can deal with PIO accesses in hi-lo/lo-hi variants. Thus, the powerpc
version of iomap.c will need to provide the same functions even
though, in this arch, they are identical to the regular
io{read|write}64 functions.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Tested-by: Horia Geantă <horia.geanta@nxp.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>