Anbernic RG-DS AW87391 Speaker Amps

Anbernic RG-DS AW87391 Speaker Amps

Merge series from Chris Morgan <macroalpha82@gmail.com>:

Add support for the Anbernic RG-DS Speaker Amplifiers. The Anbernic
RG-DS uses two AW87391 ICs at 0x58 and 0x5B on i2c2. However, the
manufacturer did not provide a firmware file, only a sequence of
register writes to each device to enable and disable them.

Add support for this *specific* configuration in the AW87390 driver.
Since we are relying on a device specific sequence I am using a
device specific compatible string. This driver does not currently
support the aw87391 for any other device as I have none to test
with valid firmware. Attempts to create firmware with the AwinicSCPv4
have not been successful.