clk: imx: add i.MX8MN ccf driver

Add i.MX8MM ccf driver support.
Modifed from Linux Kernel 5.3.0-rc1, drop some entries
that not used in U-Boot and adapt to U-Boot CCF style.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Lukasz Majewski <lukma@denx.de>