relearning. Specifically, add subcommands to mfiutil(8) which allow the
user to set the BBU and autolearn modes when the firmware supports it,
and add a subcommand which kicks off a battery relearn.
Reviewed by: sbruno, rstone
Tested by: sbruno
Approved by: rstone (co-mentor)
MFC after: 2 weeks
Sponsored by: Sandvine Incorporated