[MLIR] Reformat the Bazel build

This patch normalizes formatting of the the root BUILD.bazel file by: 1) adjusting indentation a little bit, 2) alphabetically ordering dependencies. These small deviations were introduced by some yesterday's patches:
  * https://reviews.llvm.org/D151104
  * https://reviews.llvm.org/D151346
  * https://reviews.llvm.org/rG16fe2b37365c00b0c6d0ed22c2e6521f2d5de01a
  * https://reviews.llvm.org/rG4d1cd1d8caab13d6b76ce6fc4ff76a01a7931c34

Reviewed By: aartbik

Differential Revision: https://reviews.llvm.org/D151499