net: macb: Add on the fly CPU endianness detection

Program management descriptor's access mode according to the
dynamically detected CPU endianness.

Signed-off-by: Arun Chandran <achandran@mvista.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Tested-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>