Add charge control limit to the power supply subsystem of the Compal
platform driver.

This apparently was present in the original driver by Cezary Jackiewicz
at http://eko.one.pl/index.php?page=compal-laptop but it seems to have been
overlooked.

The Kconfig description is updated to reflect this addition. It now also
mentions the hwmon interface that was already present.
Signed-off-by: Roald Frederickx <roald.frederickx@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>