DMA transactions should only only need to call io_config only once, but
block mode might call it several times to setup several transactions so
it can handle reads/writes larger than the max size per transaction, so
we move the call to the do_ functions.

This is just refactoring, there should be no functional change
Signed-off-by: NMatthew McClintock <mmcclint@codeaurora.org>
Signed-off-by: NVaradarajan Narayanan <varada@codeaurora.org>
Signed-off-by: NMark Brown <broonie@kernel.org>