selftests: mlxsw: Add PCI reset test

Test that PCI reset works correctly by verifying that only the expected
reset methods are supported and that after issuing the reset the ifindex
of the port changes.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>