media: vimc: enumerate data link entities for clarity

The data_links array was hard to read and understand. By implementing
enumerated vimc data link entities, clarity has been improved when
defining data_links. This therefore should help new programmers to
understand the codebase better. There is no functional change intended.

Suggested-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Daniel Oakley <daniel.oakley@ideasonboard.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>