target/xtensa: Include "qemu/timer.h" to use NANOSECONDS_PER_SECOND

Since d0ce7e9c the dc232b structure uses the NANOSECONDS_PER_SECOND
definition from "qemu/timer.h".  Include it to allow further includes
cleanup.
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20180528232719.4721-7-f4bug@amsat.org>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

target/xtensa/core-dc232b.c

@@ -30,6 +30,7 @@
 #include "exec/exec-all.h"
 #include "exec/gdbstub.h"
 #include "qemu/host-utils.h"
+#include "qemu/timer.h"
 
 #include "core-dc232b/core-isa.h"
 #include "overlay_tool.h"