Move ro.gfx.* properties to graphics_config_prop

To clean up bad context names exported*_prop.

Bug: 155844385
Test: boot and see no denials
Change-Id: Ie92e4293b8271bc137222a4c21637c740b06e156
diff --git a/private/system_server.te b/private/system_server.te
index 7fe6f0b..c2b4234 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -883,6 +883,9 @@
 # Set persist.adb.tls_server.enable property
 set_prop(system_server, system_adbd_prop)
 
+# Read ro.gfx.* properties
+get_prop(system_server, graphics_config_prop)
+
 # Allow invoking tools like "timeout"
 allow system_server toolbox_exec:file rx_file_perms;