clk: imx: clk-imx6ul: add clk support for imx6ull

imx6ull is the derived SoC from imx6ul

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Bai Ping <ping.bai@nxp.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>