bnxt_en: Add partno to devlink info_get cb

Add part number info from the vital product data to info_get command
via devlink tool. Update bnxt.rst documentation as well.

Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/devlink/bnxt.rst

@@ -51,6 +51,9 @@ The ``bnxt_en`` driver reports the following versions
    * - Name
      - Type
      - Description
+   * - ``board.id``
+     - fixed
+     - Part number identifying the board design
    * - ``asic.id``
      - fixed
      - ASIC design identifier