spi: Build coverage cleanups and improvements

Merge series from Mark Brown <broonie@kernel.org>:

This series opens up build coverage of a bunch of SPI drivers by
allowing build under COMPILE_TEST where possible, while also adding
appropriate architecture specific dependencies to a couple of drivers
that didn't have them so they don't show up in builds when they're not
useful.  We also have one fix for the dependencies of the s3c24xx driver
which was turned up in the process of doing this.