tests: coverage depends on native applications

Build with coverage enabled for any other boards or applications is
useless at least right now. Make sure we only enable coverage for native
applications.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/tests/Kconfig b/tests/Kconfig
index 35ca7c4..f4b8389 100644
--- a/tests/Kconfig
+++ b/tests/Kconfig
@@ -15,6 +15,7 @@
 
 config COVERAGE
 	bool "Create coverage data"
+	depends on NATIVE_APPLICATION
 	default n
 	help
 	  This option will build your application with the -coverage option