grant priv_app access to /dev/mtp_usb

android.process.media needs access to mtp_usb when MTP is enabled.

Bug: 25074672
Change-Id: Ic48a3ba8e4395104b0b957f7a9bad69f0e5ee38e

priv_app.te

@@ -12,6 +12,9 @@ bluetooth_domain(priv_app)
 # to their sandbox directory and then execute.
 allow priv_app app_data_file:file rx_file_perms;
 
+# android.process.media uses /dev/mtp_usb
+allow priv_app mtp_device:chr_file rw_file_perms;
+
 # Allow the allocation and use of ptys
 # Used by: https://play.privileged.com/store/apps/details?id=jackpal.androidterm
 create_pty(priv_app)