Move SystemUI to /system_ext

we plan to forbid hidden API in product partition.
So this app should be moved to /system_ext because it uses hidden API.
It is not permanent, so they can be moved back to /product due to
needs if there isn't hidden usage anymore.

Bug: 137908189
Test: m
Test: check whether device boots successfully
Test: atest SystemUITests
Change-Id: I54f86496d4a0045af3576091cce00e5cd285b4f8
diff --git a/data/etc/Android.bp b/data/etc/Android.bp
index 43f65e3..6bde0ed 100644
--- a/data/etc/Android.bp
+++ b/data/etc/Android.bp
@@ -128,7 +128,7 @@
 
 prebuilt_etc {
     name: "privapp_whitelist_com.android.systemui",
-    product_specific: true,
+    system_ext_specific: true,
     sub_dir: "permissions",
     src: "com.android.systemui.xml",
     filename_from_src: true,