dm: core: Add a new api to get indexed device address

Add new api to get device address based on index.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Acked-by: Jagan Teki <jteki@openedev.com>
[Rebased on master]
Signed-off-by: Jagan Teki <jteki@openedev.com>