system: use nec-usb-xhci instead of qemu-xhci

There is a bug in qemu-xhci which causes the USB bus to sometimes
disconnect. It may be related to MSI being turned off by default for
qemu-xhci and turned on by default for nec-usb-xhci but this is
unproven.

Fixes #3194

Managers/UTMQemuSystem.m

@@ -442,7 +442,7 @@ static size_t sysctl_read(const char *name) {
     if (!self.configuration.inputLegacy) {
         if ([self.configuration.systemTarget hasPrefix:@"virt"]) {
             [self pushArgv:@"-device"];
-            [self pushArgv:@"qemu-xhci,id=usb-bus"];
+            [self pushArgv:@"nec-usb-xhci,id=usb-bus"];
         } else {
             [self pushArgv:@"-usb"];
         }