[media] mt9v011: Added exposure for mt9v011

There are problems when you use this camera/sensor in a very bright room
or outside. The image is completely white, because it is overexposed.
The driver uses a default value which is not suitable for all
environments.

This patch makes it possible to adjust the exposure time by youself. I
found out by logging the i2c-data, that the windows driver for this
sensor is doing this, too. I tested the camera on a sunny day and after
adjusting the exposure time, I was able to see a very good image.

Tested-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Johannes Obermaier <johannes.obermaier@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>