x86/mm: Do not set page's count_info directly

x86/mm: Do not set page's count_info directly

Page offline patch add several flag to page_info->count_info. However,
currently some code will try to set count_info after alloc_domheap_pages
without using "&" or "|" operation, this may cause the new flags lost, since
there are no protection. This patch try to make sure all write to
count_info will only impact specific field.

Also currently shadow code assume count_info is 0 for shadow page,
however, this is invalid after the new flags. Change some assert in
shadow code.

Signed-off-by: Jiang, Yunhong <yunhong.jiang@intel.com>