net/mlx5: Provide an alternative VF upper bound for ECPF

ECPF doesn't support SR-IOV, but an ECPF E-Switch manager shall know
the max VFs supported by its peer host PF in order to control those
VF vports.

The current driver implementation uses the total vfs quantity as
provided by the pci sub-system for an upper bound of the VF vports
the e-switch code needs to deal with. This obviously can't work as
is on ECPF e-switch manager. For now, we use a hard coded value of
128 on such systems.

Signed-off-by: Bodong Wang <bodong@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>