Support configure the pcie_root_ports number for StratoVirt hypervisor

[flyflypeng]

What would you like to be added?

Support the following config field in the config_stratovirt.toml file

...
[hypervisor]
...
pcie_root_ports = 15
...

Why is this needed?

Currently, StratoVirt virt type machine only supports hotplug pci/pcie devices in the pcie-root-port device, so we need to add the specified number pcie-root-port devices configuration into the stratovirt process command line.

Inorder to add more flexibility for supporting configure the number of pcie-root-port devices for VM, add the new configuration field in the toml file for StratoVirt hypervisor.