Add a sysctl to export the EFI memory map along with a handler in the
sysctl(8) binary to format it.

Reviewed by:	emaste
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D771


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271495 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f