google/reef: Add Maxim98357a support

Adds Maxim98357a support for reef using the generic driver
in drivers/generic/max98357

Change-Id: I333d4e810e42309ac76dd90c19f05cf3e3a517e0
Signed-off-by: Sathyanarayana Nujella <sathyanarayana.nujella@intel.com>
Reviewed-on: https://review.coreboot.org/15435
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
2 files changed