Add notifier function for PLL0 clock. In the function, the cpu_root clock
should be operated by saving its current parent and setting a new safe
parent (osc clock) before setting the PLL0 clock rate. After setting PLL0
rate, it should be switched back to the original parent clock.

Fixes: e2c510d6 ("riscv: dts: starfive: Add cpu scaling for JH7110 SoC")
Cc: stable@vger.kernel.org
Reviewed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Xingyu Wu <xingyu.wu@starfivetech.com>
Link: https://lore.kernel.org/r/20240826080430.179788-2-xingyu.wu@starfivetech.comReviewed-by: Hal Feng <hal.feng@starfivetech.com>
Tested-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>