[media] si2168: add FE_CAN_MULTISTREAM into caps

PLP selection was implemented for Si2168 last month (patchwork 25387). However, FE_CAN_MULTISTREAM was not added to dvb_frontend_ops of si2168. This patch adds FE_CAN_MULTISTREAM, which indicates that multiple PLP are supported.

Signed-off-by: Olli Salonen <olli.salonen@iki.fi>
Acked-by: Antti Palosaari <crope@iki.fi>
Reviewed-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>