xhci: tweak limits

Set maxports to 15.  This is what the usb3 route string can handle.

Set maxslots to 64.  This is more than the number of root ports we
can have, but with additional hubs you can end up with more devices.

Set maxintrs (aka msi vectors) to 16.  Should be enougth, especially
considering that vectors are a limited ressource.  Linux guests use
only three at the moment.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/usb/hcd-xhci.c

@@ -37,12 +37,12 @@
 #define FIXME() do { fprintf(stderr, "FIXME %s:%d\n", \
                              __func__, __LINE__); abort(); } while (0)
 
-#define MAXPORTS_2 8
-#define MAXPORTS_3 8
+#define MAXPORTS_2 15
+#define MAXPORTS_3 15
 
 #define MAXPORTS (MAXPORTS_2+MAXPORTS_3)
-#define MAXSLOTS MAXPORTS
-#define MAXINTRS MAXPORTS
+#define MAXSLOTS 64
+#define MAXINTRS 16
 
 #define TD_QUEUE 24