x86: Make use of pagetable_get_mfn() where appropriate

x86: Make use of pagetable_get_mfn() where appropriate

... instead of the opencoded _mfn(pagetable_get_pfn(...)) construct.

Fix two overly long lines; no functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>
Release-acked-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>
Acked-by: Kevin Tian <kevin.tian@intel.com>