ASoC: samsung: wolfson: Improve compile test coverage

While the the Wolfson machine drivers have a runtime dependency on a
specific machine there is no compile time dependency. Allow to lets those
drivers to be selected when COMPILE_TEST is selected to improve the compile
time test coverage.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>