pm2301: LPN mode control support

The AC charger plug-in detection while booting causes I2C read
failure if AC charger is not connected. Now the LPN pin is enabled
for every PM2301 register access, which solves the issue.

Signed-off-by: Rupesh Kumar <rupesh.kumar@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Marcus COOPER <marcus.xm.cooper@stericsson.com>
Reviewed-by: Vijaya Kumar K-1 <vijay.kilari@stericsson.com>
Reviewed-by: Rabin VINCENT <rabin.vincent@stericsson.com>
Reviewed-by: Jonas ABERG <jonas.aberg@stericsson.com>
Tested-by: Jonas ABERG <jonas.aberg@stericsson.com>

drivers/power/pm2301_charger.h

@@ -493,6 +493,7 @@ struct pm2xxx_charger {
 	int old_vbat;
 	int failure_case;
 	int failure_input_ovv;
+	unsigned int lpn_pin;
 	struct pm2xxx_interrupts *pm2_int;
 	struct ab8500_gpadc *gpadc;
 	struct regulator *regu;