hw/i386/vmport: fix missing definitions with non-log trace backends

When compiled with anything other than the 'log' trace backend, we have:

   error: implicit declaration of function 'qemu_log_mask'
   error: 'LOG_UNIMP' undeclared (first use in this function)

This patch adds the missing include.

Fixes: 7299e1a4
       ("hw/i386/vmport: replace fprintf() by trace events or LOG_UNIMP")
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>
Message-id: 20171221211103.30311-1-laurent@vivier.eu
[PMM: fixed commit message description of when problem occurs]
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/i386/vmport.c

@@ -27,6 +27,7 @@
 #include "hw/i386/pc.h"
 #include "sysemu/hw_accel.h"
 #include "hw/qdev.h"
+#include "qemu/log.h"
 #include "trace.h"
 
 #define VMPORT_CMD_GETVERSION 0x0a