recovery: Move a few int to bool.

Most of the changes are trivial.

Also update a dead reference to device_handle_key() in device.h comment,
and add some comments to get_menu_selection() function.

Test: `mmma bootable/recovery`
Change-Id: I59ef9213ec88ab35c0e7b8a7813ccf9c56dbd5c5

device.cpp

@@ -60,7 +60,7 @@ Device::BuiltinAction Device::InvokeMenuItem(int menu_position) {
   return menu_position < 0 ? NO_ACTION : MENU_ACTIONS[menu_position];
 }
 
-int Device::HandleMenuKey(int key, int visible) {
+int Device::HandleMenuKey(int key, bool visible) {
   if (!visible) {
     return kNoAction;
   }