riscv: dts: jh7110: Add clock source from PLL

Change the PLL clock source from syscrg to sys_syscon child node.

Signed-off-by: Xingyu Wu <xingyu.wu@starfivetech.com>
Signed-off-by: Hal Feng <hal.feng@starfivetech.com>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>