arm64: zynqmp: Fix sgmii clock input freq for p-a2197

Input frequency for sgmii is 125MHz on all Xilinx designs.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/87153c59cc526f5955b3bff3db11027b5848c042.1634302099.git.michal.simek@xilinx.com