imx_ccm: Rearrange clock control module driver

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.

Reviewed by: manu
Sponsored by: The FreeBSD Foundations
Differential Revision: https://reviews.freebsd.org/D46641