soc: amlogic: meson-ee-pwrc: add support for Meson8/Meson8b/Meson8m2

This adds support for the power domains on Meson8/Meson8b/Meson8m2.
Meson8 doesn't use any reset lines while Meson8b and Meson8m2 use the
same set of reset lines (which is different from the newer SoCs).
Add dedicated compatible strings for Meson8, Meson8b and Meson8m2 to
support these differences.

Notable differences between Meson8 and G12A are:
- there is no HHI_VPU_MEM_PD_REG2 on the 32-bit SoCs
- the Meson8b datasheet describes an "audio DSP memory" power domain
  which is used for the hardware audio decoder
- the "amlogic,ao-sysctrl" only includes the power management related
  registers on the 32-bit SoCs, meaning the for example the
  AO_RTI_GEN_PWR_SLEEP0 register is at offset (0x2 << 2) rather than
  (0x3a << 2). As result of this (0x38 << 2) is subtracted from the
  register offsets, which is the start of the power management related
  registers.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20200515204709.1505498-4-martin.blumenstingl@googlemail.com