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

apps/plugins/text_viewer/text_viewer.c

@@ -97,6 +97,10 @@ enum plugin_status plugin_start(const void* file)
 #ifdef TV_AUTOSCROLL_PRE
                 if (lastbutton != TV_AUTOSCROLL_PRE)
                     break;
+#endif
+#ifdef TV_AUTOSCROLL2
+                /* fallthrough */
+            case TV_AUTOSCROLL2:
 #endif
                 autoscroll = !autoscroll;
                 break;