x86/p2m: please Clang after making certain parts HVM-only

x86/p2m: please Clang after making certain parts HVM-only

Move a few #ifdef-s, to account for diagnostics like

p2m.c:549:1: error: non-void function does not return a value in all control paths [-Werror,-Wreturn-type]

which appear despite paging_mode_translate() resolving to constant
"false" when !HVM. All of the affected functions are intended to become
fully HVM-only anyway, with their non-translated stub handling split off
elsewhere.

Fixes: 8d012d3ddffc ("x86/p2m: {get,set}_entry hooks and p2m-pt.c are HVM-only")
Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>