bnx2: Update firmware and version

Update MIPS firmware to 6.2.1, with improved small packet performance
in RSS mode, and iSCSI CID allocation bug fix on 5708.

Update driver version to 2.0.21.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>