JIT: optimize for the common case of unquantized psq_l/st

Optimistically assume used GQRs are 0 in blocks that only use one GQR, and
bail at the start of the block and recompile if that assumption fails.

Many games use almost entirely unquantized stores (e.g. Rebel Strike, Sonic
Colors), so this will likely be a big performance improvement across the board
for games with heavy use of paired singles.

Source/Core/Core/PowerPC/JitInterface.h

@@ -13,7 +13,8 @@ namespace JitInterface
 {
 	enum class ExceptionType
 	{
-		EXCEPTIONS_FIFO_WRITE
+		EXCEPTIONS_FIFO_WRITE,
+		EXCEPTIONS_PAIRED_QUANTIZE
 	};
 
 	void DoState(PointerWrap &p);