[media] smiapp: provide g_skip_top_lines method in sensor ops

Some sensors (like the one in Nokia N900) provide metadata in the first
couple of lines. Make that information information available to the
pipeline.

Use u16 instead, this is a 16-bit value.

Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>