Can not create VM in KVM on ppc64le

Issue

• When creating a VM on ppc64le by virt-install in RHEL 8, it cannot be successful with an error like the below:

ERROR    internal error: qemu unexpectedly closed the monitor: 2021-03-09T14:25:24.693052Z qemu-kvm: Requested count cache flush assist capability level not supported by kvm, try appending -machine cap-ccf-assist=off

• And if add "--machine cap-ccf-assist=off" then it will have blew error：

ERROR    Host does not support domain type kvm with machine 'cap-ccf-assist=off' for virtualization type 'hvm' arch 'ppc64le'