clk: sifive: Factor-out PLL library as separate module

To match SiFive clock driver with latest Linux, we factor-out PLL
library as separate module under drivers/clk/analogbits.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
9 files changed