Document more clearly that a probe routine:

Should have no side effects
	Must not hold resources when it returns
	May be called multiple times if it returns < 0.

Remove the bad advise that the probe routine should look for children
for devices that implement busses.  This is more properly reserved for
the attach routine.

share/man/man9/DEVICE_PROBE.9

@@ -64,15 +64,14 @@ In particular, it must not assume that any values stored in
 the softc structure will be available for its attach method and any
 resources allocated during probe must be released and re-allocated
 if the attach method is called.
-If a success code of zero is
-returned, the driver can assume that it will be the one attached.
+In addition it is an absolute requirement that the probe routine have
+no side effects whatsoever.
+The probe routine may be called more than once before the attach
+routine is called.
 .Pp
-Devices which implement busses should use this method to probe for
-the existence of devices attached to the bus and add them as
-children.
-If this is combined with the use of
-.Xr bus_generic_attach 9
-the child devices will be automatically probed and attached.
+If a success code of zero is
+returned, the driver can assume that it will be the one attached, but
+must not hold any resources when the probe routine returns.
 .Sh RETURN VALUES
 A value equal to or less than zero indicates success, greater than
 zero indicates an error (errno). For values equal to or less than
@@ -81,6 +80,7 @@ for a value less than zero, the lower the value the lower the
 priority, e.g. -100 indicates a lower priority than -50.
 .Sh SEE ALSO
 .Xr device 9 ,
+.Xr DEVICE_ATTACH 9 ,
 .Xr DEVICE_DETACH 9 ,
 .Xr DEVICE_IDENTIFY 9 ,
 .Xr DEVICE_SHUTDOWN 9