spi: qup: refactor spi_qup_io_config into two functions

This is in preparation for handling transactions larger than
64K-1 bytes in block mode, which is currently unsupported and
quietly fails.

We need to break these into two functions 1) prep is
called once per spi_message and 2) io_config is called
once per spi-qup bus transaction

This is just refactoring, there should be no functional
change

Signed-off-by: Matthew McClintock <mmcclint@codeaurora.org>
Signed-off-by: Varadarajan Narayanan <varada@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>