arm64: zynqmp: Add PHY description for SGMII on vck190 SC

SGMII requires phy to be configured. The support for this has been added to
Linux and U-Boot already that's why also describe the phy via DT. Clock is
coming from si5332 chip (output 1) 125MHz which is only one GT line use on
this board.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/8ad8d0c2fc9690cc90f95feddf87b0e94a685a43.1652262769.git.michal.simek@amd.com