docs/machine: Start to update for esp8266 port.

docs/library/machine.rst

@@ -14,6 +14,8 @@ Reset related functions
    Resets the device in a manner similar to pushing the external RESET
    button.
 
+.. only:: port_wipy
+
     .. function:: reset_cause()
 
        Get the reset cause. See :ref:`constants <machine_constants>` for the possible return values.
@@ -41,6 +43,12 @@ Power related functions
 
 .. function:: freq()
 
+    .. only:: not port_wipy
+
+        Returns CPU frequency in hertz.
+
+    .. only:: port_wipy
+
         Returns a tuple of clock frequencies: ``(sysclk,)``
         These correspond to: