Disable building of TLK, to unbreak master build.

TLK is currently pulling in bionic headers, even though it doesn't use
bionic. As a result, changes in those headers in AOSP have broken the
build. TLK should not depend on bionic at all, and should have
everything needed to build in its own headers. Fixing that is
non-trivial, so this disables building of TLK while the ryu team and
nvidia fix it properly.

Change-Id: I770609a445d184f5e0f60bbf1963e994b5bba6ce
diff --git a/device.mk b/device.mk
index cae653a..c004704 100644
--- a/device.mk
+++ b/device.mk
@@ -26,7 +26,7 @@
 # prebuilts.  To force using the prebuilt while having the source, set:
 # SECURE_OS_BUILD=false
 ifeq ($(wildcard vendor/nvidia/dragon-tlk/tlk),vendor/nvidia/dragon-tlk/tlk)
-    SECURE_OS_BUILD ?= tlk
+    SECURE_OS_BUILD ?= client_only
 endif
 
 ifeq ($(TARGET_PREBUILT_KERNEL),)