[media] v4l: vsp1: Always enable virtual RPF when BRU is in use

Regardless of a number of inputs, we should always enable virtual RPF
when BRU is used. This allows the case when there's only one input to
BRU, and a size of the input is smaller than a size of an output of BRU.

Signed-off-by: Takanari Hayama <taki@igel.co.jp>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>