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>
diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
index 719b9b8..f0ced49 100644
--- a/drivers/clk/Makefile
+++ b/drivers/clk/Makefile
@@ -8,6 +8,7 @@
 obj-$(CONFIG_$(SPL_TPL_)CLK) += clk_fixed_rate.o
 obj-$(CONFIG_$(SPL_TPL_)CLK) += clk_fixed_factor.o
 
+obj-y += analogbits/
 obj-y += imx/
 obj-y += tegra/
 obj-$(CONFIG_ARCH_ASPEED) += aspeed/