[media] rtl28xxu: generalize streaming control

Move rtl2831u LED from streaming control to power control. It
changes LED behavior slightly but who cares :)
After that same streaming control can be used for both rtl2831u
and rtl2832u.

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