virtchnl: Added support to exchange additional speed values

Introduced a new virtchnl capability flag and a struct to support exchange
of additional supported speeds.

Signed-off-by: Yashaswini Raghuram Prathivadi Bhayankaram <yashaswini.raghuram.prathivadi.bhayankaram@intel.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>