Add support for none ACPI battery method batteries

Remove the requirement that a device be a ACPI method battery to be supported
as a battery.

Require now that the device be in the battery devclass and implement the
get_status and get_info functions. This allows batteries which are not ACPI
method batteries to be supported.

Reviewed by: jtl
Approved by: jtl (mentor)
MFC after: 1 Month
Differential Revision: https://reviews.freebsd.org/D17434