MLCE-77 Depthwise Convolution with depth multiplier > 1 doesn't work

MLCE-77 Depthwise Convolution with depth multiplier > 1 doesn't work

 * Unified ArmNN's weight format to [ M, I, H, W ] for the depthwise convolution
 * Added conversion utilities to permute/reshape the weights as appropriate
   when using CL and Neon backends
 * Updated the reference implementation of the convolution
 * Updated the relevant unit tests accordingly

!android-nn-driver:459

Change-Id: I07d0818efa9d1ca1e5dad82983aac1fe78eadb18