net/mlx5: Maintain separate page trees for ECPF and PF functions

Pages for the host PF and ECPF were stored in the same tree, so the ECPF
pages were being freed along with the host PF's when the host driver
unloaded.

Combine the function ID and ECPF flag to use as an index into the
x-array containing the trees to get a different tree for the host PF and
ECPF.

Fixes: c6168161

 ("net/mlx5: Add support for release all pages event")
Signed-off-by: Daniel Jurgens <danielj@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>