spi/s3c64xx: Convert to using core message queue

Convert the s3c64xx driver to using the new message queue factored out of
the pl022 driver by Linus Walleij, saving us a nice block of code and
getting the benefits of improvements implemented in the core.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>