MFC 304492,310721,310734: Update cxgbe info in NOTES.

304492:
Move cxgb and cxgbe down to the non-mii PCI NIC section.

310721:
Mention T6 and 100GbE in description of cxgbe.

310734:
Note that the Chelsio T6 also supports 25Gbps.

To avoid overflowing 80 columns, condense the cxgbe description a bit.