Now, we create vcpus while VM being created in hypervisor. The
create vcpu hypercall will not be used any more. For compatbility,
keep the hypercall HC_CREATE_VCPU do nothing.
v4: Don't remove HC_CREATE_VCPU hypercall, let it do nothing.
Tracked-On: #3663
Signed-off-by: Shuo A Liu <shuo.a.liu@intel.com>