SPU: Use REP MOVSB in do_dma_transfer

- Try to use REP MOVSB when the size of the transfer is above a certain threshold
- This threshold is determined by the ERMS and FSRM cpuid flags
- The threshold values are (roughly) taken from GLIBC
- A threshold of 0xFFFFFFFF indicates that the cpu has neither flag

rpcs3/util/sysinfo.cpp

@@ -138,6 +138,38 @@ bool utils::has_fma4()
 	return g_value;
 }
 
+bool utils::has_erms()
+{
+	static const bool g_value = get_cpuid(0, 0)[0] >= 0x7 && (get_cpuid(7, 0)[1] & 0x200) == 0x200;
+	return g_value;
+}
+
+bool utils::has_fsrm()
+{
+	static const bool g_value = get_cpuid(0, 0)[0] >= 0x7 && (get_cpuid(7, 0)[3] & 0x10) == 0x10;
+	return g_value;
+}
+
+u32 utils::get_rep_movsb_threshold()
+{
+	static const u32 g_value = []()
+	{
+		u32 thresh_value = 0xFFFFFFFF;
+		if (has_fsrm())
+		{
+			thresh_value = 2047;
+		}
+		else if (has_erms())
+		{
+			thresh_value = 4095;
+		}
+
+		return thresh_value;
+	}();
+
+	return g_value;
+}
+
 std::string utils::get_cpu_brand()
 {
 	std::string brand;