dnn: introduce dnn operand (in c code) to hold operand infos within network

dnn: introduce dnn operand (in c code) to hold operand infos within network

the info can be saved in dnn operand object without regenerating again and again,
and it is also needed for layer split/merge, and for memory reuse.

to make things step by step, this patch just focuses on c code,
the change within python script will be added later.

Signed-off-by: Guo, Yejun <yejun.guo@intel.com>
Signed-off-by: Pedro Arthur <bygrandao@gmail.com>