clk:starfive:Set PLL2 frequency when clock tree registering

clk:starfive:Set PLL2 frequency when clock tree registering

In the file drivers/clk/starfive/clk-starfive-jh7110-pll.h,
If set PLL2_DEFAULT_FREQ NULL of 0 , then PLL2 frequency is original.
If set PLL2_DEFAULT_FREQ one of 'starfive_pll2_freq_value', then PLL2
frequency will be set the new rate during clock tree registering.

Signed-off-by: xingyu.wu <xingyu.wu@starfivetech.com>