spi: spi-ep93xx: use the default master transfer queueing mechanism

Update this driver to the default implementation of transfer_one_message().
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Mark Brown <broonie@kernel.org>