imx_ccm: Rearrange clock control module driver

[thj]

Summary

Rearrange the IMX clock control module driver so it is more straight
forward to support clock trees from other SOCs in the family.

Move the existing imx8mq_ccm driver to a more generic imx_ccm (based on
rk_cru) and update the previous driver to sub class imx_ccm.

Rename files to be consistent and fix include guards to match source
files.

Test Plan

I don't have hardware to test the impact of this on imx8mq, but the D46641 adds
support for imx8mp which I do have hardware for.

[manu]

LGTM