console: make QMP screendump use coroutine Hi, Thanks to recent work by Kevin, it becomes possible to run HMP/QMP commands in a coroutine. The screendump command is a good target, as it requires to re-enter the main-loop in ordre to flush the display, and write to file in a non-blocking way. Despite the flush, the dump may still have glitches. The graphic device may perform some operations during the write on the same framebuffer. Doing a memory copy could help, but it would also create a number of other issues. Keeping the BQL would defeat a number of advantages of using a coroutine. Afaik, there is no mechanism to "freeze" the device either (and this could also have bad consequences anyway). Good enough?