tmf: Merge the two statesystem-getting methods into one

tmf: Merge the two statesystem-getting methods into one

Use Collections.unmodifiableMap() to return a map directly,
instead of using two separate methods.

Also changed the declared type to a LinkedHashMap, so that
the order of iteration remains constant.

Change-Id: I876be06ea550d1244da87215e58fddee95f6de3d
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/11659
Tested-by: Hudson CI
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
IP-Clean: Patrick Tasse <patrick.tasse@gmail.com>