Add new fields in the FADT, required by IASL 20140926-64.

The new IASL from the recent acpi-ca import will error out
if it doesn't see these new fields, which were previously
reserved.

Reported by:	lme
Reviewed by:	neel


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272481 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f