net/mlx5: Add pages debugfs

Add pages debugfs to expose the following counters for debuggability:
fw_pages_total - How many pages were given to FW and not returned yet.
vfs_pages - For SRIOV, how many pages were given to FW for virtual
functions usage.
host_pf_pages - For ECPF, how many pages were given to FW for external
hosts physical functions usage.

Signed-off-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>