[media] vb2: add a dev field to use for the default allocation context

The allocation context is nothing more than a per-plane device pointer
to use when allocating buffers. So just provide a dev pointer in vb2_queue
for that purpose and drivers can skip allocating/releasing/filling in
the allocation context unless they require different per-plane device
pointers as used by some Samsung SoCs.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Sakari Ailus <sakari.ailus@iki.fi>
Cc: Florian Echtler <floe@butterbrot.org>
Cc: Federico Vaga <federico.vaga@gmail.com>
Cc: "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
Cc: Scott Jiang <scott.jiang.linux@gmail.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Fabien Dessenne <fabien.dessenne@st.com>
Acked-by: Benoit Parrot <bparrot@ti.com>
Cc: Mikhail Ulyanov <mikhail.ulyanov@cogentembedded.com>
Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ludovic Desroches <ludovic.desroches@atmel.com>
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>