[AMDGPU] Fix handling of FP in cs.chain functions (#161194)

In case there is an dynamic alloca / an alloca which is not in the entry
block, cs.chain functions do not set up an FP, but are reported to need
one. This results in a failed assertion in
`SIFrameLowering::emitPrologue()` (Assertion `(!HasFP || FPSaved) &&
"Needed to save FP but didn't save it anywhere"' failed.) This commit
changes `hasFPImpl` so that the need for an SP in a cs.chain function
does not directly imply the need for an FP anymore.

This LLVM defect was identified via the AMD Fuzzing project.

Author: ro-i

llvm/lib/Target/AMDGPU/SIFrameLowering.cpp

@@ -2170,7 +2170,9 @@ bool SIFrameLowering::hasFPImpl(const MachineFunction &MF) const {
     return MFI.getStackSize() != 0;
   }
 
-  return frameTriviallyRequiresSP(MFI) || MFI.isFrameAddressTaken() ||
+  return (frameTriviallyRequiresSP(MFI) &&
+          !MF.getInfo<SIMachineFunctionInfo>()->isChainFunction()) ||
+         MFI.isFrameAddressTaken() ||
          MF.getSubtarget<GCNSubtarget>().getRegisterInfo()->hasStackRealignment(
              MF) ||
          mayReserveScratchForCWSR(MF) ||