[mlir][linalg] Support permutation when lowering to loop nests

[mlir][linalg] Support permutation when lowering to loop nests

Linalg ops are perfect loop nests. When materializing the concrete
loop nest, the default order specified by the Linalg op's iterators
may not be the best for further CodeGen: targets frequently need
to plan the loop order in order to gain better data access. And
different targets can have different preferences. So there should
exist a way to control the order.

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D91795