clk: imx: add pfdv2 support

The pfdv2 is designed for PLL Fractional Divide (PFD) observed in System
Clock Generation (SCG) module in IMX ULP SoC series. e.g. i.MX7ULP.

NOTE pfdv2 can only be operated when clk is gated.

Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Anson Huang <Anson.Huang@nxp.com>
Cc: Bai Ping <ping.bai@nxp.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
[sboyd@kernel.org: Include clk.h for sparse warnings]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>