[AMDGPU] NFC: Add helper to query archVGPR (#102690)

For any users that is interested in just the ArchVGPR count (without
comparing to AGPR count)

Author: jrbyrnes

llvm/lib/Target/AMDGPU/GCNRegPressure.h

@@ -46,14 +46,20 @@ struct GCNRegPressure {
 
   void clear() { std::fill(&Value[0], &Value[TOTAL_KINDS], 0); }
 
+  /// \returns the SGPR32 pressure
   unsigned getSGPRNum() const { return Value[SGPR32]; }
+  /// \returns the aggregated ArchVGPR32, AccVGPR32 pressure dependent upon \p
+  /// UnifiedVGPRFile
   unsigned getVGPRNum(bool UnifiedVGPRFile) const {
     if (UnifiedVGPRFile) {
       return Value[AGPR32] ? alignTo(Value[VGPR32], 4) + Value[AGPR32]
                            : Value[VGPR32] + Value[AGPR32];
     }
     return std::max(Value[VGPR32], Value[AGPR32]);
   }
+  /// \returns the ArchVGPR32 pressure
+  unsigned getArchVGPRNum() const { return Value[VGPR32]; }
+  /// \returns the AccVGPR32 pressure
   unsigned getAGPRNum() const { return Value[AGPR32]; }
 
   unsigned getVGPRTuplesWeight() const { return std::max(Value[VGPR_TUPLE],