x86/shadow: l3table[] and gl3e[] are HVM only

x86/shadow: l3table[] and gl3e[] are HVM only

... by the very fact that they're 3-level specific, while PV always gets
run in 4-level mode. This requires adding some seemingly redundant
#ifdef-s - some of them will be possible to drop again once 2- and
3-level guest code doesn't get built anymore in !HVM configs, but I'm
afraid there's still quite a bit of disentangling work to be done to
make this possible.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>