[media] rtl2832: add platform data callbacks for exported resources

Add callback for all of those functions which are currently
exported using EXPORT_SYMBOL. That allows us convert every user to
callbacks and eventually all exported symbols could be removed.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>