ARM: dts: meson: add the AO ARC remote processor

The 32-bit Amlogic Meson SoCs embed an ARC processor in the Always-On
power domain which is typically used for managing system suspend. The
memory for this ARC core is taken from the AHB SRAM area. Depending on
the actual SoC a different ARC core is used:
- Meson6 and earlier: some ARCv1 ISA based core (probably an ARC625)
- Meson8 and later: an ARC EM4 (ARCv2 ISA) based core

Add the device-tree node for this remote-processor along with the
required SRAM sections, clocks and reset-lines. Also use the
SoC-specific compatible string to manage any differences (should
they exist).

On Meson8, Meson8b and Meson8m2 the "secbus2" IO region is needed as
some bits need to be programmed there. Add this IO region for those
SoCs as well.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20210102205904.2691120-6-martin.blumenstingl@googlemail.com