mb/google/volteer: Add keyboard layout to fw_config

A new field was defined for different keyboard layouts, so add this field
to the list and provide the two options that were defined.

Change-Id: Ic357446725e34221040705929d54cbce94c5ab8b
Signed-off-by: Duncan Laurie <dlaurie@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47478
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/mainboard/google/volteer/variants/baseboard/devicetree.cb

@@ -38,6 +38,10 @@ fw_config
 		option SD_GL9755S 1
 		option SD_RTS5261 2
 	end
+	field KB_LAYOUT 20 21
+		option KB_LAYOUT_DEFAULT 0
+		option KB_LAYOUT_1 1
+	end
 end
 
 chip soc/intel/tigerlake