Currently cloud-hypervisor supports hotplug of CPUs, passthrough devices, virtio devices and memory resizing,
but in hotplug.md it still mentiones: "Currently Cloud Hypervisor only supports hot plugging of CPU devices."
We need to remove the incorrect information from hotplug.md to reflect the true situation.
Fixes: #3504
Signed-off-by: Liang Zhou <zhoul110@chinatelecom.cn>