x86, efi: Set runtime_version to the EFI spec revision

x86, efi: Set runtime_version to the EFI spec revision

commit 712ba9e9afc4b3d3d6fa81565ca36fe518915c01 upstream.

efi.runtime_version is erroneously being set to the value of the
vendor's firmware revision instead of that of the implemented EFI
specification. We can't deduce which EFI functions are available based
on the revision of the vendor's firmware since the version scheme is
likely to be unique to each vendor.

What we really need to know is the revision of the implemented EFI
specification, which is available in the EFI System Table header.

Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>