net/mlx5: Use dma device access helper

Use the PCI device directly for dma accesses as non PCI device unlikely
support IOMMU and dma mappings.
Introduce and use helper routine to access DMA device.

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