hack: imx8m-ddrc: Set AHB and MAIN_AXI clocks together with DRAM freq
This is what NXP kernels do to achieve low power modes. See https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/soc/imx/busfreq-imx8mq.c?h=imx_5.4.70_2.3.0 and https://source.codeaurora.org/external/imx/linux-imx/tree/arch/arm64/boot/dts/freescale/imx8mq.dtsi?h=imx_5.4.70_2.3.0#n267
all credits go to @sebastian.krzyszkowiak as I only cleaned up https://source.puri.sm/Librem5/linux-next/-/merge_requests/434 because of his vacation plans.