[mlir] add permutation utility

I found myself typing this code several times at different places
by now, so time to make this a general utility instead. Given
a permutation, it returns the permuted position of the input,
for example (i,j,k) -> (k,i,j) yields position 1 for input 0.

Reviewed By: ftynse

Differential Revision: https://reviews.llvm.org/D108347