ASoC: WM8991: Add initial WM8991 driver

The WM8991 is a highly integrated ultra-low power hi-fi CODEC designed for
handsets rich in multimedia features such as GPS, mobile TV, digital audio
playback and gaming.

This driver was originally written by Graeme Gregory and has been maintained
out of tree by Mark Brown and Dimitris Papastamos.

Signed-off-by: Graeme Gregory <gg@opensource.wolfsonmicro.com>
Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
diff --git a/sound/soc/codecs/Kconfig b/sound/soc/codecs/Kconfig
index 61e36ef..a18cff4 100644
--- a/sound/soc/codecs/Kconfig
+++ b/sound/soc/codecs/Kconfig
@@ -77,6 +77,7 @@
 	select SND_SOC_WM8985 if SND_SOC_I2C_AND_SPI
 	select SND_SOC_WM8988 if SND_SOC_I2C_AND_SPI
 	select SND_SOC_WM8990 if I2C
+	select SND_SOC_WM8991 if I2C
 	select SND_SOC_WM8993 if I2C
 	select SND_SOC_WM8994 if MFD_WM8994
 	select SND_SOC_WM8995 if SND_SOC_I2C_AND_SPI
@@ -308,6 +309,9 @@
 config SND_SOC_WM8990
 	tristate
 
+config SND_SOC_WM8991
+	tristate
+
 config SND_SOC_WM8993
 	tristate