x86, vmx: Enable EPT (Extended PageTable) support on new Intel processors.

x86, vmx: Enable EPT (Extended PageTable) support on new Intel processors.

We use the EPT page table as P2M (guest physical to machine
mapping), removing the linear page table when EPT is used for the
domain (see the new file p2m-ept.c). We did this by adding three
operations in the p2m_domain. If VT-d is enabled, the EPT page table
will be used as the VT-d page table as well (i.e. shared).

Signed-off-by: Xin Li <xin.b.li@intel.com>
Signed-off-by: Jun Nakajima <jun.nakajima@intel.com>
Signed-off-by: Xiaohui Xin <Xiaohui.xin@intel.com>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>