Add vendor_overlay support to fsgen

Test: m with
PRODUCT_COPY_FILES += \
    audio_policy_configuration.xml:$(TARGET_COPY_OUT_PRODUCT)/vendor_overlay/34/etc/audio_policy_configuration.xml

Change-Id: I854245e5a56a79c0e4ea473665adaf32c4106e10
diff --git a/android/neverallow.go b/android/neverallow.go
index a7bfd2d..794b393 100644
--- a/android/neverallow.go
+++ b/android/neverallow.go
@@ -381,6 +381,7 @@
 			"prebuilt_first_stage_ramdisk",
 			"prebuilt_radio",
 			"prebuilt_gpu",
+			"prebuilt_vendor_overlay",
 		).
 		DefinedInBpFile().
 		Because("module type not allowed to be defined in bp file")