bnxt_en: Fix asic.rev in devlink dev info command

The current asic.rev is incomplete and does not include the metal
revision.  Add the metal revision and decode the complete asic
revision into the more common and readable form (A0, B0, etc).

Fixes: 7154917a

 ("bnxt_en: Refactor bnxt_dl_info_get().")
Reviewed-by: Edwin Peer <edwin.peer@broadcom.com>
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>