staging: most: core: separate property showing links

Currently an AIM has the following properties available to manage links:
  - write-only "remove_link" used to remove a link from a list
  - read/write "add_link" used to add a link to a list and display them

This patch transfers the read functionality of "add_link" to the new
read-only property "links" to build consistent set of properties to control
the list of links.

Signed-off-by: Andrey Shvetsov <andrey.shvetsov@k2l.de>
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>