Temporarily re-add IAR for K64F

The Travis check for each PR still uses K64F to test IAR configs.
In the future, we should remove IAR tests.

Author: LDong-Arm

targets/targets.json

@@ -693,7 +693,8 @@
         "core": "Cortex-M4F",
         "supported_toolchains": [
             "ARM",
-            "GCC_ARM"
+            "GCC_ARM",
+            "IAR"
         ],
         "extra_labels_add": [
             "Freescale",
@@ -763,6 +764,9 @@
             "gcc_arm": [
                 "std",
                 "small"
+            ],
+            "iar": [
+                "std"
             ]
         },
         "supported_application_profiles": [