net: xilinx: axi_mrmac: Add MRMAC driver

Add support for xilinx multirate(MRMAC) ethernet driver.
This driver uses multichannel DMA(MCDMA) for data transfers of MRMAC.
Added support for 4 ports of MRMAC for speeds 10G and 25G.
MCDMA supports upto 16 channels but in this driver we have setup only
one channel which is enough.

Tested 10G and 25G on all 4 ports.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>