cxgb4: update API for TP indirect register access

Try to access TP indirect registers via firmware first.  If this fails,
fallback and access them directly.  This ensures that driver and
firmware do not conflict each other while accessing the TP indirect
registers.

Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>