[media] msi3101: add sampling mode control

Whilst Quadrature Sampling is most common sampling technique used in
radio technology there is others too. Add control user could select
sampling mode. We currently support only quadrature sampling.

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