Add support for the Meson GX SoCs to the meson-ee-pwrc driver.

The power domains on the GX SoCs are very similar to G12A. The only
known differences so far are:
- The GX SoCs do not have the HHI_VPU_MEM_PD_REG2 register (for the
  VPU power-domain)
- The GX SoCs have an additional reset line called "dvin"
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20200515204709.1505498-5-martin.blumenstingl@googlemail.com