Add information about reset gpio for ethernet phy in case someone wants to
use it.
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/e153f0cda37a2a6ea1c6e11fb0a4af1d400f29e2.1623684253.git.michal.simek@xilinx.com