Currently, guest_linear_to_real to_real() in vmxassist assumes guest HVM
use 2 level page table when entering protect mode with PG enabled. Vista
uses 3 level (PAE enabled) page table, so memory addressing is wrong.
This patch fixes it, by considering all 4 possible cases.
Signed-off-by: Xiaowei Yang <xiaowei.yang@intel.com>