[llvm] [AMDGPU] Make max dwords of memory cluster configurable (PR #119342)

[via llvm-commits]

ruiling wrote:

> > > function attribute
> > 
> > 
> > Thanks! What's the suggested way to access that value in function attribute from the SIInstrInfo? Maybe keep a record of that value in MachineFunctionInfo and get from it?
> 
> That's just a matter of caching it in MFI or whether read directly from the IR attribute. In either case, the MachineFunction needs to be passed into the hook

Added a function attribute for it, do we want to keep the command line option for it?

https://github.com/llvm/llvm-project/pull/119342