MLK-10803 media: mxc: vout: fix the race condition for multiple disaplay

There will some race condition such as the followings:

- multiple open concurrence will cause the vout refer to the stall vout-> v4l_wq
  or the vout-> v4l_wq is not initialized correctly.
- multiple open concurrence will cause the global fb setting race-condition,
  thus, it will have the “set_crop error exceeds width/height” or
  “mxc_v4l2_output v4l2_out.30: can not find output”

This patch fix the above issue by adding the protection for the critical section.

Reviewed-by: Liu Ying <b17645@freescale.com>
Signed-off-by: Jason Liu <r64343@freescale.com>