cxgb4: Use FW LDST cmd to access TP_PIO_{ADDR, DATA} register first

The TP_PIO_{ADDR,DATA} registers are are in conflict with the firmware's
use of these registers. Added a routine to access it through FW LDST
cmd.
Access all TP_PIO_{ADDR,DATA} register access through new routine if FW
is alive. If firmware is dead, than fall back to indirect access.

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>