[llvm] [MIPS] Use same logic as Clang when setting setMaxAtomicSizeInBitsSupported (PR #124218)

[YunQiang Su via llvm-commits]

================
@@ -519,10 +519,12 @@ MipsTargetLowering::MipsTargetLowering(const MipsTargetMachine &TM,
   setTargetDAGCombine({ISD::SDIVREM, ISD::UDIVREM, ISD::SELECT, ISD::AND,
                        ISD::OR, ISD::ADD, ISD::SUB, ISD::AssertZext, ISD::SHL});
 
-  if (Subtarget.isGP64bit())
+  if (ABI.IsN32() || ABI.IsN64())
----------------
wzssyqa wrote:

And if we do something like
```
clang -mabi=32 -march=mips64r2
```
may be we wish set it to 64 here.

https://github.com/llvm/llvm-project/pull/124218