arm64: defconfig: enable meson gx audio as module

Enable the module config for the Amlogic GX audio card.
This module will imply the internal components usually associated
with it to make a functional sound card on these platforms.

Also enable the simple amplifier module which often used on the
output stage of those cards.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Tested-by: Christian Hewitt <christianshewitt@gmail.com>
Link: https://lore.kernel.org/r/20200421163935.775935-2-jbrunet@baylibre.com