pm2301-charger: Support for over voltage protection on the ab9540

Added support for main charger over voltage protection.

Signed-off-by: Rupesh Kumar <rupesh.kumar@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Philippe LANGLAIS <philippe.langlais@stericsson.com>
Tested-by: Michel JAOUEN <michel.jaouen@stericsson.com>