Define gpu_service and allow surfaceflinger to provide it

Bug: 26620936 and 27352427
Change-Id: I3d6d2e479d95133693790a97827e45e9dd30bc4a
diff --git a/service_contexts b/service_contexts
index 9b049e3..c1fe961 100644
--- a/service_contexts
+++ b/service_contexts
@@ -43,6 +43,7 @@
 android.hardware.fingerprint.IFingerprintDaemon u:object_r:fingerprintd_service:s0
 gfxinfo                                   u:object_r:gfxinfo_service:s0
 graphicsstats                             u:object_r:graphicsstats_service:s0
+gpu                                       u:object_r:gpu_service:s0
 hardware                                  u:object_r:hardware_service:s0
 hardware_properties                       u:object_r:hardware_properties_service:s0
 hdmi_control                              u:object_r:hdmi_control_service:s0