ASoC: cs35l35: Add for configuring drive mode in unused slots

Add support for setting how the I2S pins are driven in unused slots,
currently the chip will just use the default of drive 0, however this
causes issues when multiple devices are attached to the same bus.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Acked-by: Brian Austin <brian.austin@cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/cs35l35.h

@@ -190,6 +190,10 @@
 #define CS35L35_AMP_GAIN_ZC_MASK	0x10
 #define CS35L35_AMP_GAIN_ZC_SHIFT	4
 
+/* CS35L35_SP_FMT_CTL3 */
+#define CS35L35_SP_I2S_DRV_MASK		0x03
+#define CS35L35_SP_I2S_DRV_SHIFT	0
+
 /* Class H Algorithm Control */
 #define CS35L35_CH_STEREO_MASK		0x40
 #define CS35L35_CH_STEREO_SHIFT		6