net: stmmac: add ethtool per-queue irq statistic support

Adding ethtool per-queue statistics support to show number of interrupts
generated at DMA tx and DMA rx. All the counters are incremented at
dwmac4_dma_interrupt function.

Signed-off-by: Vijayakannan Ayyathurai <vijayakannan.ayyathurai@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>