Sprinkle const around where appropriate (#1909)

* Sprinkle `const` around where appropriate

- This will make it easier to use `NDS` objects in `const` contexts (e.g. `const` parameters or methods)

* Remove the `const` qualifier on `DSi_DSP::DSPRead16`

- MMIO reads can be non-pure, so this may not be `const` in the future

src/JitBlock.h

@@ -46,12 +46,12 @@ public:
 
     JitBlockEntry EntryPoint;
 
-    u32* AddressRanges()
-    { return &Data[0]; }
-    u32* AddressMasks()
-    { return &Data[NumAddresses]; }
-    u32* Literals()
-    { return &Data[NumAddresses * 2]; }
+    const u32* AddressRanges() const { return &Data[0]; }
+    u32* AddressRanges() { return &Data[0]; }
+    const u32* AddressMasks() const { return &Data[NumAddresses]; }
+    u32* AddressMasks() { return &Data[NumAddresses]; }
+    const u32* Literals() const { return &Data[NumAddresses * 2]; }
+    u32* Literals() { return &Data[NumAddresses * 2]; }
 
 private:
     TinyVector<u32> Data;