Enable ptp_kvm module for time synchronization

[hiroaki mizuguchi]

I want to use ptp_kvm module for time synchronization.

reference: https://opensource.com/article/17/6/timekeeping-linux-vms

tested on ubuntu kvm image: https://cloud-images.ubuntu.com/impish/20211103/impish-server-cloudimg-amd64-disk-kvm.img

```
ubuntu@test:~$ lsb_release -rd
Description: Ubuntu 21.10
Release: 21.10
ubuntu@test:~$ dpkg -l linux-image-kvm
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-===============-=============-============-=======================================
ii linux-image-kvm 5.13.0.1005.5 amd64 Linux kernel image for virtual systems.
ubuntu@test:~$ grep -i ptp /boot/config-5.13.0-1005-kvm
CONFIG_HAVE_OPTPROBES=y
CONFIG_NF_CONNTRACK_PPTP=m
CONFIG_NF_NAT_PPTP=m
# PTP clock support
# CONFIG_PTP_1588_CLOCK is not set
# end of PTP clock support
```

use case

1. load ptp_kvm module
2. udev make /dev/ptp_kvm symlink to /dev/ptpX by /usr/lib/udev/rules.d/50-udev-default.rules
3. chrony use /dev/ptp_kvm for time synchronization

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Matt Feinstein (lnx-solutions)]

need a kvm/virtual/minimal image(s) that includes this from 20.04 and up