Permit loading of efirt module even when there's no EFI to call. The
module loading is successful, but attempts to use it will not be
successful. This is similar to what we do (did?) with ACPI on non-ACPI
systems. We succeed if we can't find the necessary information to hook
into EFI, but still fail if we're unable to allocate resources if we
do find EFI.

Not Objected to by: kib@
MFC Afer: 3 days