neuron: ch_haven: Add support for svm device tree format

The secondary vm device tree will have a different format than the
primary vm. Try parsing the node as a secondary vm node if the
shared-buffer region does not exist.

Change-Id: Id794a1b21507329f4e16f1335a17a2262ecabd5a
Signed-off-by: Chris Lew <clew@codeaurora.org>