dnnl: init at 1.1.2

This commit continues the work proposed in #68014, and provides an entirely FOSS
variant of the `dnnl` package. Updates to add an `mkl` flavor will be added
later, pending discussion about the cleanest way to overlay this consistently.

Fixes #67982, closes #68014

Co-authored-by: Alex Rice <alexrice999@hotmail.co.uk>