Add inference engine private data support

Add inference engine private data support

[Version] : 0.5.2
[Issue type] : new feature

Add inference engine private data support. As for this, This patch adds
a new enumeration and structure to the inference_engine_type.h header file
to manage private data in an inference engine.

With this patch, we can deliver inference engine specific data to
each inference engine backend.

Change-Id: I2cbb015aa4262315982adcc5c6119ada7cad543f
Signed-off-by: Inki Dae <inki.dae@samsung.com>