ASoC: wm8741: Add differential mono mode support

The WM8741 DAC supports several differential output modes (stereo,
stereo reversed, mono left, mono right). Add platform data and DT
bindings to configure it.

Signed-off-by: Sergej Sawazki <ce3a@gmx.de>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/wm8741.h

@@ -194,6 +194,12 @@
 #define WM8741_DITHER_SHIFT                          0  /* DITHER - [1:0] */
 #define WM8741_DITHER_WIDTH                          2  /* DITHER - [1:0] */
 
+/* DIFF field values */
+#define WM8741_DIFF_MODE_STEREO                      0  /* stereo normal */
+#define WM8741_DIFF_MODE_STEREO_REVERSED             2  /* stereo reversed */
+#define WM8741_DIFF_MODE_MONO_LEFT                   1  /* mono left */
+#define WM8741_DIFF_MODE_MONO_RIGHT                  3  /* mono right */
+
 /*
  * R32 (0x20) - ADDITONAL_CONTROL_1
  */
@@ -208,4 +214,8 @@
 
 #define  WM8741_SYSCLK 0
 
+struct wm8741_platform_data {
+	u32 diff_mode;   /* Differential Output Mode */
+};
+
 #endif