x86/hvm: disable pkeys for guests in non-paging mode

x86/hvm: disable pkeys for guests in non-paging mode

This patch disables pkeys for guest in non-paging mode, However XEN always uses
paging mode to emulate guest non-paging mode, To emulate this behavior, pkeys
needs to be manually disabled when guest switches to non-paging mode.

Signed-off-by: Huaitong Han <huaitong.han@intel.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>