wm831x: Factor out WM831x backup battery charger

The backup battery on WM831x is a separate IP block to the main PMU
and is largely unrelated to the main supply functionality. Factor it
out into a separate driver in order to reflect this and better support
future hardware versions.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>
diff --git a/drivers/mfd/wm831x-core.c b/drivers/mfd/wm831x-core.c
index 49b7885..6a35f2a 100644
--- a/drivers/mfd/wm831x-core.c
+++ b/drivers/mfd/wm831x-core.c
@@ -794,6 +794,9 @@
 
 static struct mfd_cell wm8310_devs[] = {
 	{
+		.name = "wm831x-backup",
+	},
+	{
 		.name = "wm831x-buckv",
 		.id = 1,
 		.num_resources = ARRAY_SIZE(wm831x_dcdc1_resources),
@@ -947,6 +950,9 @@
 
 static struct mfd_cell wm8311_devs[] = {
 	{
+		.name = "wm831x-backup",
+	},
+	{
 		.name = "wm831x-buckv",
 		.id = 1,
 		.num_resources = ARRAY_SIZE(wm831x_dcdc1_resources),
@@ -1081,6 +1087,9 @@
 
 static struct mfd_cell wm8312_devs[] = {
 	{
+		.name = "wm831x-backup",
+	},
+	{
 		.name = "wm831x-buckv",
 		.id = 1,
 		.num_resources = ARRAY_SIZE(wm831x_dcdc1_resources),