media: test-drivers: Set REQBUFS minimum number of buffers

Instead of using 'min_queued_buffers' field to specify the
minimum number of buffers to be allocated when calling REQBUF
use 'min_reqbufs_allocation' field which is dedicated to this
purpose.

Change the minimum requested buffers to 2 for vivid-meta-out
and vivid-touch-cap drivers when creating the queues.
That allows to remove code which prohibe to allocate only
one buffer in their respective queue setup functions.

While at it rename vivid_create_queue() parameter.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>