cxgb4: support new ISSI flash parts

Add support for new 32MB and 64MB ISSI (Integrated Silicon
Solution, Inc.) FLASH parts.

Signed-off-by: Casey Leedom <leedom@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>