clk: imx: add ckil clock for i.MX7

Add the necessary clock to use the ckil on i.MX7.

Inspired from the following patch:
https://github.com/boundarydevices/linux-imx6/commit/b80e8271



Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>