soc: riscv: sifive-freedom: Get coreclk and peripheral clock from DTS.

Rather than specify input clock for each peripheral individually, instead
specify the relevant clocks in DTS.

This will enable easier support for non-default coreclk on fe310 in a
follow-up CL.

Signed-off-by: Shawn Nematbakhsh <shawn@rivosinc.com>
18 files changed