riscv: dts: jh7110: Enable PLL node in SPL

Previously PLL node was missing from SPL dts. This caused BUS_ROOT
to stay on OSC clock (24Mhz). As a result, all peripherals have to
run at a much lower frequency, and loading from sdcard/emmc is slow.
Thus, enabling PLL node in dts to fix this.

Signed-off-by: Bo Gan <ganboing@gmail.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>