The power domains on the 32-bit Meson8/Meson8b/Meson8m2 SoCs are very
similar to what G12A still uses. The (known) differences are:
- Meson8 doesn't use any reset lines at all
- Meson8b and Meson8m2 use the same reset lines, which are different
  from what the 64-bit SoCs use
- there is no "vapb" clock on the older SoCs
- amlogic,ao-sysctrl cannot point to the whole AO sysctrl region but
  only the power management related registers

Add a new compatible string and adjust clock and reset line expectations
for each SoC.
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200515204709.1505498-2-martin.blumenstingl@googlemail.com