[MLIR][SCF] Simplify scf.if by swapping regions if condition is a not

Given an if of the form, simplify it by eliminating the not and swapping the regions

scf.if not(c) {
  yield origTrue
} else {
  yield origFalse
}

becomes

scf.if c {
  yield origFalse
} else {
  yield origTrue
}

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D116990