Rename domain "system" to "system_server".

Now that the "system" domain is just about the system_server, it's
clearer if the domain is called "system_server".

This CL depends on the renaming in external/sepolicy performed in
https://android-review.googlesource.com/#/c/65502/

Change-Id: I90a6850603dcf60049963462c5572d36de62bc00
diff --git a/sepolicy/system_server.te b/sepolicy/system_server.te
new file mode 100644
index 0000000..50564e4
--- /dev/null
+++ b/sepolicy/system_server.te
@@ -0,0 +1,5 @@
+allow system_server knv_device:chr_file rw_file_perms;
+allow system_server sysfs_devices_system_cpu:file w_file_perms;
+allow system_server sysfs_devices_system_cpu:dir r_dir_perms;
+allow system_server elan_ip_device:chr_file rw_file_perms;
+allow system_server diag_device:chr_file rw_file_perms;