ice: Introduce and use ice_vsi_type_str

ice_vsi_type_str converts an ice_vsi_type enum value to its string
equivalent. This is expected to help easily identify VSI types from
module print statements.

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>