build: Consolidate the crypto_utils presence tests

No point checking filesystem repeatedly/check may change in future

Change-Id: I0413b07b850f785eb5150c6ed18836cc56e94d6f
diff --git a/Android.mk b/Android.mk
index 582b710..9719918 100644
--- a/Android.mk
+++ b/Android.mk
@@ -302,6 +302,8 @@
         LOCAL_SHARED_LIBRARIES += libe4crypt
     endif
 endif
+WITH_CRYPTO_UTILS := \
+    $(if $(wildcard system/core/libcrypto_utils/Android.mk),true)
 ifeq ($(TW_USE_MODEL_HARDWARE_ID_FOR_DEVICE_ID), true)
     LOCAL_CFLAGS += -DTW_USE_MODEL_HARDWARE_ID_FOR_DEVICE_ID
 endif