qemu: Add qemu xen logic for Xen HVM S3 resume

This patch is qemu patch 2 to fix Xen HVM S3 bug, adding qemu
xen logic. When qemu wakeup, qemu xen logic is notified and
hypercall to xen hypervisor to unpause domain.

Signed-off-by: Liu Jinsong <jinsong.liu@intel.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>