net: zynq: Add support for PHY configuration in SGMII mode

SGMII configuration depends on proper GT setting that's why when node has
phys property call PSGTR driver to configure it properly.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Sean Anderson <seanga2@gmail.com>
Link: https://lore.kernel.org/r/bbc8d7ed9d308199168e4455c7a3e3a5ac0890e7.1639562397.git.michal.simek@xilinx.com