[media] rtl28xxu: add SDR module for devices having R828D tuner

Load SDR sub-driver in order to support SDR for devices having
this tuner too.

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