aes_util: Allow SetIV to be non-allocating

In a few places, the data to be set as the IV is already within an array.
We shouldn't require this data to be heap-allocated if it doesn't need
to be. This allows certain callers to reduce heap churn.

src/core/crypto/ctr_encryption_layer.h

@@ -4,7 +4,8 @@
 
 #pragma once
 
-#include <vector>
+#include <array>
+
 #include "core/crypto/aes_util.h"
 #include "core/crypto/encryption_layer.h"
 #include "core/crypto/key_manager.h"
@@ -14,18 +15,20 @@ namespace Core::Crypto {
 // Sits on top of a VirtualFile and provides CTR-mode AES decription.
 class CTREncryptionLayer : public EncryptionLayer {
 public:
+    using IVData = std::array<u8, 16>;
+
     CTREncryptionLayer(FileSys::VirtualFile base, Key128 key, std::size_t base_offset);
 
     std::size_t Read(u8* data, std::size_t length, std::size_t offset) const override;
 
-    void SetIV(const std::vector<u8>& iv);
+    void SetIV(const IVData& iv);
 
 private:
     std::size_t base_offset;
 
     // Must be mutable as operations modify cipher contexts.
     mutable AESCipher<Key128> cipher;
-    mutable std::vector<u8> iv;
+    mutable IVData iv{};
 
     void UpdateIV(std::size_t offset) const;
 };