ENGR00259949 mxc vout:fix screen tearing issue in ic bypass case

ENGR00259949 mxc vout:fix screen tearing issue in ic bypass case

In ic bypass case, we put video buffers at a framebuffer display
channel directly. The display channel works at triple buffer
mode. To make sure a video buffer(buf N) has been shown on display
device, we at least need to wait for the second video buffer(buf N+2)
after the current buffer(buf N) is put on the display channel. Then,
the current buffer(buf N) can be added to the dequeue list, otherwise,
the user may get the buffer too early so that the buffer being shown
can be overwritten - screen tearing issue happens.

Signed-off-by: Liu Ying <Ying.Liu@freescale.com>