bnx2x: Add new 57840 device IDs

The 57840 boards come in two flavours: 2 x 20G and 4 x 10G.
To better differentiate between the two flavours, a separate device ID
was assigned to each.
The silicon default value is still the currently supported 57840 device ID
(0x168d), and since a user can damage the nvram (e.g., 'ethtool -E')
the driver will still support this device ID to allow the user to amend the
nvram back into a supported configuration.

Notice this patch contains lines longer than 80 characters (strings).

Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>