x86/nested-svm: Update the paging mode on VMRUN and VMEXIT emulation.

x86/nested-svm: Update the paging mode on VMRUN and VMEXIT emulation.

This allows Xen to walk the l1 hypervisor's shadow pagetable
correctly.  Not needed for hap-on-hap guests because they are handled
at lookup time.  Problem found with 64bit Win7 and 32bit XPMode where Win7
switches forth and back between long mode and PAE legacy pagetables.

Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>
[Adjusted to update in all cases where the l1 vmm uses shadows]
Signed-off-by: Tim Deegan <tim@xen.org>
Committed-by: Tim Deegan <tim@xen.org>