arm64: dts: socfpga: agilex: fix dtbs_check warning for f2s-free-clk
The f2s-free-clk requires a clock-frequency value. We put in an
arbitrary value of 100 MHz for a constant. The true clock frequency
would get generated in an FPGA design and the bootloader will populated
in actual hardware designs.
This fixes warning like this:
arch/arm64/boot/dts/intel:34:8
4 f2s-free-clk (fixed-clock): 'clock-frequency' is a required property