media: drivers/media/common/videobuf2: rename from videobuf

This directory contains the videobuf2 framework, so name the
directory accordingly.

The name 'videobuf' typically refers to the old and deprecated
videobuf version 1 framework so that was confusing.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>