[mlir][NFC] Remove trailing whitespaces from `*.td` and `*.mlir` files.

This is generated by running

```
sed --in-place 's/[[:space:]]\+$//' mlir/**/*.td
sed --in-place 's/[[:space:]]\+$//' mlir/**/*.mlir
```

Reviewed By: rriddle, dcaballe

Differential Revision: https://reviews.llvm.org/D138866