ASoC: Implement interrupt based WM8994 microphone detection

Support interrupt based microphone bias detection. The WM8994 has two
microphone bias supplies, with detection supported on both. Detection
using GPIOs together with the standard GPIO based jack framework is
already supported via the platform data for the WM8994 core driver.

Note that as well as the microphone bias itself the system clock and
whichever AIF clock is supplying the system clock will need to be
enabled for detection to function.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/wm8994.h

@@ -23,4 +23,7 @@ extern struct snd_soc_dai wm8994_dai[];
 #define WM8994_FLL1 1
 #define WM8994_FLL2 2
 
+int wm8994_mic_detect(struct snd_soc_codec *codec, struct snd_soc_jack *jack,
+		      int micbias, int det, int shrt);
+
 #endif