sepolicy: qcom: Allow reading PSU sysfs by system_server

BatteryService queries the usb state to check whether the usb type
is HVDCP. This patch adds a rule to allow that.

For more context check BatteryService#Led#isHvdcpPresent.

Change-Id: Ifacf13dde4b1df81c92bf5d92196e504e61dd402

sepolicy/qcom/system_server.te

@@ -4,3 +4,7 @@ allow system_server mm-pp-daemon:unix_stream_socket connectto;
 
 # Time services
 allow system_server time_daemon:unix_stream_socket connectto;
+
+#allow reading of usb sysfs to query hvdcp state
+allow system_server sysfs_usb_supply:dir { search };
+allow system_server sysfs_usb_supply:file r_file_perms;