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/analogbits/Kconfig b/drivers/clk/analogbits/Kconfig
new file mode 100644
index 0000000..1d25e6f
--- /dev/null
+++ b/drivers/clk/analogbits/Kconfig
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config CLK_ANALOGBITS_WRPLL_CLN28HPC
+	bool