[flang] [llvm] [clang] [NFC][AMDGPU] Move address space enum to LLVM directory (PR #73944)

[Krzysztof Parzyszek via cfe-commits]

kparzysz wrote:

> I think the enum looks a bit out of place in a file called "TargetParser.h", but I'm not very familiar with this part of the project, so I'll let the experts say something if there is a more suitable location for it.

That's a good point.  The address spaces for AMDGPU are already defined [here](https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/AMDGPU/AMDGPU.h#L395-L456).  I think it makes sense to extract them into a separate file (including the static functions to query address spaces), and put that file in `llvm/include/llvm/Support`.  We already have two AMDGPU-specific files in there, so there is a precedent that we can follow.

https://github.com/llvm/llvm-project/pull/73944