Add ML Single API support of NNStreamer

Add ML Single API support of NNStreamer

This patch adds ML Single API support of NNStreamer.

On MediaVision, NNFW(in-house NN Runtime) and Vivante NPU
will be controlled by inference-engine-mlapi backend
through ML Single API of NNStreamer.

As one more backends should be controlled by the inference-engine-mlapi
backend, this patch introduces a new function, SetPluginType,
which lets ML Single API know which tensor filter - NNFW or Vivante NPU -
should be used, and adds two backend types - Vivante and NNFW.

Change-Id: Iccf9fe97f5ec50c5c1bfd7bab48927e0f343f182
Signed-off-by: Inki Dae <inki.dae@samsung.com>