cxgb4: move Tx/Rx free pages collection to common code

This information needs to be collected in vmcore device dump as well.
So, move to common code.

Fixes: fa145d5d

 ("cxgb4: display number of rx and tx pages free")
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>