Test: Add TEST_SKIPPED result in test_status_t

Some test case may be skipped in runtime when the test environment
is unavailable. TEST_SKIPPED is added to replace TEST_FAILED when
the issue comes from condition check.

Signed-off-by: Jianliang Shen <jianliang.shen@arm.com>
Change-Id: I36bdef342d6ce6ef844f49e6185e17f50f48231d
diff --git a/test/framework/test_framework.h b/test/framework/test_framework.h
index c205614..c01c34d 100644
--- a/test/framework/test_framework.h
+++ b/test/framework/test_framework.h
@@ -23,6 +23,7 @@
 enum test_status_t {
     TEST_PASSED = 0,  /*!< Test has passed */
     TEST_FAILED = 1,  /*!< Test has failed */
+    TEST_SKIPPED = 2, /*!< Test has skipped */
 };
 
 struct test_result_t {