* - Added support optimized bn mkldnn implementation in cpu emitter
- modified bn unit_test to support new implementation
- added layout assignment for bn op
- Style Fix

(cherry picked from commit 7747a40806d62c126059d5c873adcd2e61a0adb0)

* modified value initilization in cpu_fusion to be float explicit

(cherry picked from commit 03499d380073d0197ab8cbd154eb03f63b042a48)

* fix compilation issue

* Addressed PR comments
- added exception if gamma and beta layout isnot equal to memory::format::x
- throw exception if bn Op is not mkldnn op

* fix compilation issue

* added support to handle multiple o/ps in fprop bn fusion

* - Removed laytout pass for bn
- fixed autodiff bug in bn
- added "Add" for the dispatcher in cpu-layout pass

* style fix

* Fix bprop batchnorm test with get_output_elements

* Style fix