ASoC: Intel: avs: Add missing audio amplifier for KBL

KBL platform is missing the definition of 'max98357a' audio amplifier.
This amplifier is used on many KBL Chromebooks, for instance variant
'nami' of 'Google/poppy' baseboard.

Reported-by: CoolStar <coolstarorganization@gmail.com>
Signed-off-by: Alicja Michalska <ahplka19@gmail.com>

Link: https://lore.kernel.org/r/Y3wHyJ/EcsLRHGr3@tora


Signed-off-by: Mark Brown <broonie@kernel.org>