[media] v4l: vsp1: Rename pipeline validate functions to pipeline build

The primary purpose of those functions is to build the pipeline, rename
them to make this clearer.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>