riscv: dts: starfive: add assigned-clock* to limit frquency

riscv: dts: starfive: add assigned-clock* to limit frquency

In JH7110 SoC, we need to go by-pass mode, so we need add the
assigned-clock* properties to limit clock frquency.

Signed-off-by: William Qiu <william.qiu@starfivetech.com>
Reviewed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>