[media] smiapp: Move enumerating available media bus codes later

As the controls creation is separated in two sections, the available media
bus codes and link frequencies can be enumerated later on.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>