This patch adds 2ms sleep after camera power down signal
is set to high or to low to ensure power down or up
is successful. OV5640/OV5642 camera specs say that they
require this condtion to be true - for PWDN to go low,
power must first become stable(DVDD to PWDN>=1ms), so
this patch simply use 2ms which should be enough.

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