[mlir] improve error handling in Linalg op splitting

[mlir] improve error handling in Linalg op splitting

In several cases, the splitting may be known to be a noop, i.e., produce
no second part. Thread this information through the transform utilities
to the transform dialect, and differentiate it from the error state.

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D141138