xrt: Add defines for minimum haptic frequency and unspecified haptic frequency

src/xrt/include/xrt/xrt_defines.h

@@ -701,6 +701,22 @@ enum xrt_output_name
 	// clang-format on
 };
 
+/*!
+ * Value used to indicate a haptic pulse of the minimal supported duration.
+ *
+ * @ingroup xrt_iface
+ */
+#define XRT_MIN_HAPTIC_DURATION -1
+
+/*!
+ * Value used to indicate a haptic pulse of some runtime defined optimal
+ * frequency.
+ *
+ * @ingroup xrt_iface
+ */
+
+#define XRT_FREQUENCY_UNSPECIFIED 0
+
 /*!
  * A union of all output types.
  *