For prelaunched VM, Service OS and postlaunched RT VM, we only need the vRTC
provides backed-up date, so we could use the simple vRTC which implemented
in hypervisor. For postlaunched VM (which is not a RT VM), we needs the device
module to emulate the vRTC for it.
Tracked-On: #1842
Signed-off-by: Li, Fei1 <fei1.li@intel.com>
Reviewed-by: Yu Wang <yu1.wang@intel.com>