media: dt-bindings: media: Add i.MX8 ISI DT bindings

The Image Sensing Interface (ISI) combines image processing pipelines
with DMA engines to process and capture frames originating from a
variety of sources. The inputs to the ISI go through Pixel Link
interfaces, and their number and nature is SoC-dependent. They cover
both capture interfaces (MIPI CSI-2 RX, HDMI RX) and memory inputs.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>