vpp_device: fix vpp device kernel driver binding

vpp_device: fix vpp device kernel driver binding

Attempt to unbind a driver from a device only if it is bound to a
driver.

Remove the dynamic addition of an existing device ID to a driver. From
the docs [0]:
Writing a device ID to this file will attempt to
dynamically add a new device ID to a PCI device driver.

Since we assume the VFs are bound to the kernel driver when VPP Device
topology creation is done, it implies that the kernel driver supports
the device ID of those VFs, removing the need to add the support.

[0]: https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-bus-pci

Change-Id: I20f3ca071a5a84a06ff358ba514532248a8f9ad0
Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>