powerpc: io.h: move iomap.h include so that it can use readq/writeq defs

Subsequent patches in this series makes use of the readq and writeq
defines in iomap.h. However, as is, they get missed on the powerpc
platform seeing the include comes before the define. This patch moves
the include down to fix this.

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