hw/i386/vmport: replace fprintf() by trace events or LOG_UNIMP

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20171215034356.4449-2-f4bug@amsat.org>
[Replace unknown command tracepoint with LOG_UNIMP, add
 generic tracepoint for vmport commands. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>