net/mlx5e: Expose PCIe statistics to ethtool

This patch exposes two groups of PCIe counters:
- Performance counters.
- Timers and states counters.
Queried with ethtool -S <devname>.

Signed-off-by: Gal Pressman <galp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>