Add setting to disable merge for specific VID/PID.

For example J-PAC in dual X-input mode with VID/PID 045e:028e

input.cpp

@@ -2724,6 +2724,11 @@ void mergedevs()
 	make_unique(0x0E8F, 0x3013, 1); // Mayflash SNES controller 2 port adapter
 	make_unique(0x16C0, 0x05E1, 1); // XinMo XM-10 2 player USB Encoder
 
+	if (cfg.no_merge_vid)
+	{
+		make_unique(cfg.no_merge_vid, cfg.no_merge_pid, (cfg.no_merge_pid ? 1 : 0));
+	}
+
 	// merge multifunctional devices by id
 	for (int i = 0; i < NUMDEV; i++)
 	{