power: isl9519q: Add pm8921 external-charger support

The isl9519q interface with the pm8921 via external-charger registration.
The pm8921 notifies the isl9519q to start/stop charging.
This way the isl9519q driver doesn't need to:
1. Monitor the charge current for end-of-charging detection.
2. Get interrupt from isl9519q HW.
3. Check n_valid_gpio for DC Inserted validity.

Change-Id: Ia0472440010fe1582a5aa8b557c9e4ab17e1a657
Signed-off-by: Amir Samuelov <amirs@codeaurora.org>
diff --git a/drivers/power/Kconfig b/drivers/power/Kconfig
index 179a4ac..cca1035 100644
--- a/drivers/power/Kconfig
+++ b/drivers/power/Kconfig
@@ -261,7 +261,8 @@
 
 config ISL9519_CHARGER
 	tristate "isl9519 charger"
-	depends on BATTERY_MSM8X60
+	depends on (BATTERY_MSM8X60 || PM8921_CHARGER)
+	depends on I2C
 	default n
 	help
 	  The isl9519q charger chip from intersil is connected to an external