[arm][cleanup] Refactor decoding to follow guide

Stick more closely to the decoding guide laid out in the manual, and
also take the chance to remove some duplicate code.

Drive-by fix a clang-tidy warning for bool literal.

Bug: v8:11074
Change-Id: I91aa8db7cd3db30b250e8bfc9bb146c8bb56dcd1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2567530
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71630}

src/execution/arm/simulator-arm.h

@@ -332,6 +332,10 @@ class Simulator : public SimulatorBase {
   void SoftwareInterrupt(Instruction* instr);
   void DebugAtNextPC();
 
+  // Helper to write back values to register.
+  void AdvancedSIMDElementOrStructureLoadStoreWriteback(int Rn, int Rm,
+                                                        int ebytes);
+
   // Stop helper functions.
   inline bool isWatchedStop(uint32_t bkpt_code);
   inline bool isEnabledStop(uint32_t bkpt_code);
@@ -391,6 +395,9 @@ class Simulator : public SimulatorBase {
   void DecodeAdvancedSIMDDataProcessing(Instruction* instr);
   void DecodeMemoryHintsAndBarriers(Instruction* instr);
   void DecodeAdvancedSIMDElementOrStructureLoadStore(Instruction* instr);
+  void DecodeAdvancedSIMDLoadStoreMultipleStructures(Instruction* instr);
+  void DecodeAdvancedSIMDLoadSingleStructureToAllLanes(Instruction* instr);
+  void DecodeAdvancedSIMDLoadStoreSingleStructureToOneLane(Instruction* instr);
   void DecodeAdvancedSIMDTwoOrThreeRegisters(Instruction* instr);
 
   void DecodeVMOVBetweenCoreAndSinglePrecisionRegisters(Instruction* instr);