mb/google/nissa: Add AUDIO_CONFIG in fw_config

The codec alc5650 has different setting from other amp codec in
depthcharge. Since nissa has a single shared depthcharge target,
add the fw_config field to allow different audio_configs.
(refer to chromium:4983866)

BUG=b:307410704
TEST=With depthcharge change, set fw_config and gbb flags on craaskana
     and check beep sound on firmware screen is workable.

Change-Id: I7446fce57557204d91151f1a31755381c1813c6f
Signed-off-by: Ren Kuo <ren.kuo@quanta.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78791
Reviewed-by: Eric Lai <ericllai@google.com>
Reviewed-by: Reka Norman <rekanorman@chromium.org>
Reviewed-by: David Wu <david_wu@quanta.corp-partner.google.com>
Reviewed-by: Tyler Wang <tyler.wang@quanta.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/brya/variants/baseboard/nissa/devicetree.cb

@@ -1,4 +1,8 @@
 fw_config
+	field AUDIO_CONFIG 28
+		option AMP_GPIO			0
+		option AMP_RT5650		1
+	end
 	field SD_BOOT 29
 		option SD_BOOT_ENABLE		0
 		option SD_BOOT_DISABLE		1