x86/hvm: Correct long mode predicate

x86/hvm: Correct long mode predicate

hvm_long_mode_enabled() tests for EFER.LMA, which is specifically different to
EFER.LME.

Rename it to match its behaviour, and have it strictly return a boolean value
(although all its callers already use it in implicitly-boolean contexts, so no
functional change).

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Tim Deegan <tim@xen.org>