YH8xx,YH9xx: Keymap improvement

The main "innovation" in this patch are two "virtual buttons"
for the record switch on YH92x targets. When the switch state
changes, a single BUTTON_REC_SW_ON or .._OFF button event will
be generated. Thus keymap code can react on switching, but
not on the actual state of the switch.

Wherever sensible, the following user scheme is applied:
- use PLAY as confirm button
- use REW button or Long REW to exit
- use REC (YH820) or FFWD (YH92X) as modifier key for button combos

Change-Id: Ic8d1db9cc6869daed8dda98990dfdf7f6fd5d5a1

manual/rockbox_interface/main.tex

@@ -504,9 +504,8 @@ detail in the following paragraph.
 
   There are three buttons at the top of the right hand side of the \dap{}: \ButtonFF{} on the top, 
   \ButtonPlay{} in the middle and \ButtonRew{} underneath. Below these buttons is the \ButtonRec{}
-  switch. When the \ButtonRec{} switch is moved towards the top of the \dap{}, it acts like
-  a pressing regular button, but it blocks other actions in this position, so it have to be set 
-  back by the user.
+  switch. Rockbox doesn't take note of the actual \emph{position} of the switch, but reacts to a 
+  \emph{switching movement} like pressing a regular button.
 
   On the top panel of the \dap{}, from left to right, you can find the following: headphone/remote 
   socket, line-in socket, internal microphone, and the \ButtonHold{} switch. Note that when the