ch: Enable hyperv hypervisor

ch: Enable hyperv hypervisor

Cloud-Hypervisor is capable of running VMs with kvm or mshv as the
hypervisor on Linux Host. Guest to hypevisor ABI with mshv hypervisor is
the same as in the case of VIR_DOMAIN_VIRT_HYPERV. So, VIR_DOMAIN_VIRT_HYPERV
type will be reused to represent the config with Linux Host and mshv as the
hypervisor.

While initializing ch driver, check if either of /dev/kvm or /dev/mshv
device is present on the host. Before starting ch domains, check if the
requested hypervisor device is present on the host.

Users can specify hypervisor in ch guests's domain definitions like
below:

<domain type='kvm'>

_or_

<domain type='hyperv'>

Signed-off-by: Praveen K Paladugu <prapal@linux.microsoft.com>
Signed-off-by: Praveen K Paladugu <praveenkpaladugu@gmail.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>