Add and install permission file for Android 9+

Without this, installing the twrp app as system app leads to
reboot loops into recovery with log messages like:
java.lang.IllegalStateException: Signature|privileged permissions not in privapp-permissions whitelist: {me.twrp.twrpapp: android.permission.READ_PRECISE_PHONE_STATE, me.twrp.twrpapp: android.permission.BATTERY_STATS, me.twrp.twrpapp: android.permission.PACKAGE_USAGE_STATS}

Change-Id: I6156323ea0d23512b0d7eefbd03aa627f3002ae8
(cherry picked from commit 86a4370e6fe4bb20033b0de3a261aec4bf3573db)
diff --git a/prebuilt/privapp-permissions-twrpapp.xml b/prebuilt/privapp-permissions-twrpapp.xml
new file mode 100644
index 0000000..9b294c2
--- /dev/null
+++ b/prebuilt/privapp-permissions-twrpapp.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<permissions>
+    <privapp-permissions package="me.twrp.twrpapp">
+        <permission name="android.permission.BATTERY_STATS"/>
+        <permission name="android.permission.PACKAGE_USAGE_STATS"/>
+        <permission name="android.permission.READ_PRECISE_PHONE_STATE"/>
+    </privapp-permissions>
+</permissions>