Introduce a simple clock driver for Exynos7870's CMU blocks, more specifically, CMU_MIF, CMU_FSYS, and CMU_PERI banks. This should be enough to serve U-Boot's minimal requirements. Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org> Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>