MAINTAINERS: power_supply: update maintainership

Take over maintanence for orphaned power supply subsystem
and assign linux-pm@vger.kernel.org as mailing list.

Signed-off-by: Sebastian Reichel <sre@kernel.org>
Acked-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>