[mlir][linalg] Add channel-first variants of convolution

This change adds the following three operations and unit tests for them:

- conv_3d_ncdhw_fcdhw
- depthwise_conv_1d_ncw_cw
- depthwise_conv_3d_ncdhw_cdhw

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D150054