settings: zms: add option to disable updating linked list

When deleting a settings entry the linked list is updated by removing
the deleted node. This operation is time consuming and add some delays.
For applications that use almost the same set of Setting entries, add an
option to make this operation faster at a cost of having some empty
nodes in the linked list.
These empty nodes can be used later when the deleted entry is written
again.
Each empty node occupies 16B of storage.

Signed-off-by: Riadh Ghaddab <rghaddab@baylibre.com>