[mlir][Linalg] Uniformize SplitReduction transforms and add option to use...

[mlir][Linalg] Uniformize SplitReduction transforms and add option to use Bufferization::AllocTensor

This revision merges the 2 split_reduction transforms and adds extra control by using attributes.

SplitReduction is known to require a concrete additional buffer to store tempoaray information.
Add an option to introduce a `bufferization.alloc_tensor` instead of `linalg.init_tensor`.
This behaves better with subset-based tiling and bufferization.

Differential Revision: https://reviews.llvm.org/D128722