spi: fsl_spi: Convert to transfer_one

Let the core handle all the chipselect bakery and replace
transfer_one_message() by transfer_one() and prepare_message().

At the time being, there is fsl_spi_cs_control() to handle
chipselects. That function handles both GPIO and non-GPIO
chipselects. The GPIO chipselects will now be handled by
the core directly, so only handle non-GPIO chipselects and
hook it to ->set_cs

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/753266abafe81722d86c3ddb8bac8ef1cb00fe8c.1660829841.git.christophe.leroy@csgroup.eu
Signed-off-by: Mark Brown <broonie@kernel.org>