Rename nvhost_writable_device to gpu_device

In particular, this allows the nakasi boot animation to
work with bootanim in enforcing, and addresses the
following fatal denials:

11.953395   type=1400 audit(1386989602.240:5): avc:  denied  { read write } for  pid=345 comm="BootAnimation" name="nvmap" dev=tmpfs ino=5305 scontext=u:r:bootanim:s0 tcontext=u:object_r:nvhost_writable_device:s0 tclass=chr_file
11.955950   type=1400 audit(1386989602.240:6): avc:  denied  { read write } for  pid=345 comm="BootAnimation" name="nvhost-ctrl" dev=tmpfs ino=5360 scontext=u:r:bootanim:s0 tcontext=u:object_r:nvhost_writable_device:s0 tclass=chr_file

Change-Id: Id2d9711ce14ec755cc48f67d89e6a726e0f7706a
diff --git a/sepolicy/system_server.te b/sepolicy/system_server.te
index 9e20aba..c3eda54 100644
--- a/sepolicy/system_server.te
+++ b/sepolicy/system_server.te
@@ -1,4 +1,4 @@
-allow system_server { knv_device nvhost_writable_device }:chr_file rw_file_perms;
+allow system_server { knv_device }:chr_file rw_file_perms;
 allow system_server sysfs_devices_system_cpu:file w_file_perms;
 allow system_server elan_ip_device:chr_file rw_file_perms;
 allow system_server diag_device:chr_file rw_file_perms;