ASoC: jz4740: Improve build test coverage

Allow the jz4740 audio drivers to be build when CONFIG_COMPILE_TEST is selected.
This should improve the build test coverage. There is one small piece of
platform dependent code in the jz4740-i2s driver. It uses the DMA request type
constants which are defined in a platform specific header. We can solve this by
moving them from the platform specific header to the I2S driver.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Mark Brown <broonie@linaro.org>