[flang] Move KindOrLen enum to common/fortran.h

This is so that it can more easily be used in semantics in the
representation of type parameters.

Original-commit: flang-compiler/f18@f734d754e49b45c8bcaf246f577b030e77413aa7
Reviewed-on: https://github.com/flang-compiler/f18/pull/173
Tree-same-pre-rewrite: false