hw/display/vmware_vga: do not discard screen updates

hw/display/vmware_vga: do not discard screen updates

In certain circumstances, typically when there is lots changing on the
screen, updates will be discarded resulting in garbled output.

This change simplifies the traversal of the display update FIFO queue
when applying updates. We just track the queue length and iterate up to
the end of the queue.

Additionally when adding updates to the queue, if the buffer reaches
capacity we force a flush before accepting further events.

Signed-off-by: Carwyn Ellis <carwynellis@gmail.com>
Message-Id: <20220206183956.10694-3-carwynellis@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>