[media] media: vb2: Take queue or device lock in mmap-related vb2 ioctl handlers

The vb2_fop_mmap() and vb2_fop_get_unmapped_area() functions are plug-in
implementation of the mmap() and get_unmapped_area() file operations
that calls vb2_mmap() and vb2_get_unmapped_area() on the queue
associated with the video device. Neither the
vb2_fop_mmap/vb2_fop_get_unmapped_area nor the
v4l2_mmap/vb2_get_unmapped_area functions in the V4L2 core take any
lock, leading to race conditions between mmap/get_unmapped_area and
other buffer-related ioctls such as VIDIOC_REQBUFS.
Fix it by taking the queue or device lock around the vb2_mmap() and
vb2_get_unmapped_area() calls.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>