ARM: imx: add clock support for imx6sl

* Clock bindings for Freescale i.MX6 SoloLite

Required properties:

- compatible: Should be "fsl,imx6sl-ccm"

- reg: Address and length of the register set

- #clock-cells: Should be <1>

The clock consumer should specify the desired clock by having the clock

ID in its "clocks" phandle cell.  See include/dt-bindings/clock/imx6sl-clock.h

for the full list of i.MX6 SoloLite clock IDs.