net/mlx5: Separate and generalize dma device from pci device

The mlx5 Sub-Function (SF) sub device will be introduced in
subsequent patches. It will be created as mediated device and
belong to mdev bus. It is necessary to treat dma operations on
PF, VF and SF in uniform way, hence reduce the dependency on
pdev pci dev struct and work directly out of newly introduced
'struct device' from previous patch.

This patch does not change any functionality.

Signed-off-by: Vu Pham <vuhuong@mellanox.com>
Reviewed-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>