ASoC: wm8904: make the driver visible in Kconfig

For platforms that use the audio-graph-card driver, the codec is
not selected by SoC-platform driver. Make it available.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>