uVisor: Define UVISOR_PRESENT based on target labels

Now there is no need any more to specify the UVISOR_PRESENT symbol from
the mbed command line tools. By using a target that has UVISOR_SUPPORTED
has a label, the uVisor-internal UVISOR_PRESENT symbol will be set
automatically.

Author: AlessandroA

features/FEATURE_UVISOR/includes/uvisor-lib/uvisor-lib.h

@@ -20,9 +20,14 @@
 /* This file translates mbed-specific pre-processor symbols into
  * uVisor-specific ones. Then the main uvisor-lib.h file is included. */
 
-/* By default uVisor is not there. */
-#if !defined(UVISOR_PRESENT)
+/* mbed uses UVISOR_SUPPORTED to determine whether the full uVisor binaries
+ * should be included or not. This symbol maps to the uVisor-internal symbol
+ * UVISOR_PRESENT. */
+/* By default uVisor is not supported. */
+#if !defined(FEATURE_UVISOR) || !defined(TARGET_UVISOR_SUPPORTED) || defined(TARGET_UVISOR_UNSUPPORTED)
 #define UVISOR_PRESENT 0
+#else
+#define UVISOR_PRESENT 1
 #endif
 
 /* Detect the target using the mbed-specific symbols and determine the MPU