hack! imx8m-ddrc: Set AHB and MAIN_AXI clocks together with DRAM freq

This is what NXP kernels do to achieve low power modes.
2 jobs for ddr in 68 minutes and 48 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #361894
librem5
build:aarch64

00:24:16

passed #361895
librem5:arm64
build:deb

01:08:48