The SPI core provides infrastructure for standard message queueing so use
that instead of handling everything in the driver. This simplifies the
driver.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com> Acked-by: Linus Walleij <linus.walleij@linaro.org> Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>