dt-bindings: net: Update Freescale TSEC to support "queue-group"

dt-bindings: net: Update Freescale TSEC to support "queue-group"

At present the Freescale TSEC node DT bindings doc requires a <reg>
property in the TSEC node. But this might not always be the case.
In the upstream Linux kernel, there is no DT bindings doc for it
but the kernel driver tests a subnode of a name prefixed with
"queue-group", as we can see from gfar_of_init():

  for_each_available_child_of_node(np, child) {
      if (!of_node_name_eq(child, "queue-group"))
  ...

in drivers/net/ethernet/freescale/gianfar.c

Update our DT bindings to describe this alternate description.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>