net/mlx5: Imply MLXFW in mlx5_core

[ Upstream commit bad861f31bb15a99becef31aab59640eaeb247e2 ]

mlxfw can be compiled as external module while mlx5_core can be
builtin, in such case mlx5 will act like mlxfw is disabled.

Since mlxfw is just a service library for mlx* drivers,
imply it in mlx5_core to make it always reachable if it was enabled.

Fixes: 3ffaabec ("net/mlx5e: Support the flash device ethtool callback")
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>