IB/mlx5: Introduce and use mlx5_core_is_vf()

[ Upstream commit e53a9d26cf80565cfb7172fc52a0dfac73613a0f ]

Instead of deciding a given device is virtual function or
not based on a device is PF or not, use already defined
MLX5_COREDEV_VF by introducing an helper API mlx5_core_is_vf().

This enables to clearly identify PF, VF and non virtual functions.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Vu Pham <vuhuong@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Stable-dep-of: e05feab22fd7 ("RDMA/mlx5: Enforce same type port association for multiport RoCE")
Signed-off-by: Sasha Levin <sashal@kernel.org>