Fixed a get/put_page mismatch for guest L2 pages. Sometimes, when you

Fixed a get/put_page mismatch for guest L2 pages.  Sometimes, when you
destroy an OS when it is in real mode, there is an extra put_page in
domain_relinquish_resource.  This causes the page be freed with
non-zero type count.  With ASSERT enabled, hypervisor will crash; with
debug=n, on some machines, the system will hang in
alloc_domheap_pages, due to type_info being a union with cpumask and
not equal to 0.

Signed-off-by: Xiaofeng Ling <xiaofeng.ling@intel.com>