usb: usbip tool: Add ncontrollers in vhci_driver structure

A new field ncontrollers is added to the vhci_driver structure.
And this field is stored by scanning the vhci_hcd* dirs in the
platform udev.

Suggested-and-reviewed-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Yuyang Du <yuyang.du@intel.com>
Acked-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>