net: thunderx: Fix IOMMU translation faults

ACPI support has been added to ARM IOMMU driver in 4.10 kernel
and that has resulted in VNIC interfaces throwing translation
faults when kernel is booted with ACPI as driver was not using
DMA API. This patch fixes the issue by using DMA API which inturn
will create translation tables when IOMMU is enabled.

Also VNIC doesn't have a seperate receive buffer ring per receive
queue, so there is no 1:1 descriptor index matching between CQE_RX
and the index in buffer ring from where a buffer has been used for
DMA'ing. Unlike other NICs, here it's not possible to maintain dma
address to virt address mappings within the driver. This leaves us
no other choice but to use IOMMU's IOVA address conversion API to
get buffer's virtual address which can be given to network stack
for processing.

Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>