The new si570 unit (570BBC000876DG) which will be used on fmc-adc-100m
board (EDA-02063-v7-0) is shipped with configuration to produce
49.870130Mhz output clock signals.

But we need 100Mhz, and thus, we need to configure the clock during the
probe of fmc-adc.

The code is ported from linux/drivers/clk/clk-si570.c
(linux-v5.10.192.rt92).
Signed-off-by: Vaibhav Gupta <vaibhav.gupta@cern.ch>