cxgb4: Update pm_stats for T6 adapter family

Updated pm_stats code to display input FIFO wait (index 5) and read
latency (index 7) counters for T6 adapters

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