V4L/DVB (13165): videobuf do not force buffer size to be multiple of PAGE_SIZE

When the image size (bytesperline*height) is not multiple
of PAGE_SIZE, v4l2 rounded the required buffer size to
be multiple of PAGE_SIZE. This prevented user space
to store images directly into userptr buffers which were
not multiple of PAGE_SIZE. This constraint is removed.

The start address is still assumed to be required
page-aligned, ie., when v4l2 allocates mmap buffers,
the offset between different buffers is page-aligned.

Signed-off-by: Tuukka Toivonen <tuukka.o.toivonen@nokia.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>