[flang] Lower function and subroutine calls

This patch introduce basic function/subroutine calls.
Because of the state of lowering only simple scalar arguments
can be used in the calls. This will be enhanced in follow up
patches with arrays, allocatable, pointer ans so on.

```
subroutine sub1()
end

subroutine sub2()
  call sub1()
end
```

This patch is part of the upstreaming effort from fir-dev branch.

Reviewed By: schweitz

Differential Revision: https://reviews.llvm.org/D120419



Co-authored-by: Eric Schweitz <eschweitz@nvidia.com>
Co-authored-by: Jean Perier <jperier@nvidia.com>
Co-authored-by: V Donaldson <vdonaldson@nvidia.com>