[mlir] Revisit `LinalgLoopDistributionOptions`.

This patch cleans up the way `LinalgLoopDistributionOptions` are meant
to be used. The option just contains a call back that takes the list
of loop ranges that represent the loops that are to be distributed.
These loops are the outer parallel loops of the tiled operation which
have non-zero tile sizes specified. The call back returns for each of
the loops,
- The procId to use,
- The number of processors,
- The distribution method to use for that loop.

Reviewed By: antiagainst, hanchung

Differential Revision: https://reviews.llvm.org/D131232