This patch creates vm_event support in HV, including:
1. Create vm_event data type.
2. Add vm_event sbuf and its initializer. The sbuf will be allocated by
DM in Service VM. Its page address will then be share to HV through
hypercall.
3. Add an API to send the HV generated event.
Tracked-On: #8547
Signed-off-by: Wu Zhou <wu.zhou@intel.com>
Reviewed-by: Junjie Mao <junjie.mao@intel.com>