add support for more devices on Meson8 and Meson8b

This series adds:
- USB support on Meson8 and Meson8b (it seems that some boards show an error when trying to initialize one of the USB2 PHYs, but we have the same problem on some GXBB boards. it is working fine for me - on a board which is not supported upstream yet)
- hardware random number generator support (Meson8 and Meson8b seem to have two 32-bit hardware random number generator registers, while the GX SoCs only have one. This is not handled by the meson-rng driver yet, but that can still be improved later on)
- SAR ADC support
- add reserved memory zones to fix random hangs when filling the memory (currently only on Meson8 until I have a Meson8b device to test if the same problem appears there as well)
- use the real ethernet clock on Meson8 and Meson8b to fix ethernet when the bootloader does not enable the gate clock
- add the SCU (Snoop Control Unit) which is needed for SMP support
- minor preparations for further .dts updates as this already exports the SDIO clocks (a driver for this MMC controller is work-in-progress) as well as the corresponding pin definitions in meson8.dtsi
- this adds the pwm_e (typically used for the 32.768 kHz LPO clock for the SDIO wifi chip) and pwm_f (used on some boards for the dimmable power LED) pins to meson8.dtsi

NOTE: the .dts changes from this series depend on my previous patch from [0]: "ARM: dts: meson8: fix the IR receiver pins"