ice: check for a leaf node presence

Check for a leaf node presence for a given VSI. This check is required
before removing a VSI since VSIs can't be removed with enabled queues
(with leaf nodes) from the FW scheduler tree unless its a reset.

Signed-off-by: Victor Raj <victor.raj@intel.com>
Reviewed-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>