remoteproc: meson-mx-ao-arc: Add a driver for the AO ARC remote procesor

Amlogic Meson6, Meson8, Meson8b and Meson8m2 embed an ARC core in the
Always-On (AO) power-domain. This is typically used for waking up the
ARM cores after system suspend.

The configuration is spread across three different registers:
- AO_REMAP_REG0 which must be programmed to zero, it's actual purpose
  is unknown. There is a second remap register which is not used in the
  vendor kernel (which served as reference for this driver).
- AO_CPU_CNTL is used to start and stop the ARC core.
- AO_SECURE_REG0 in the SECBUS2 register area with unknown purpose.

To boot the ARC core we also need to enable it's gate clock and trigger
a reset.

The actual code for this ARC core can come from an ELF binary, for
example by building the Zephyr RTOS for an ARC EM4 core and then taking
"zephyr.elf" as firmware. This executable does not have any "rsc table"
so we are skipping rproc_elf_load_rsc_table (rproc_ops.parse_fw) and
rproc_elf_find_loaded_rsc_table (rproc_ops.find_loaded_rsc_table).

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20210921192557.1610709-3-martin.blumenstingl@googlemail.com


[Fixed header file order]
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>