hw/core/clock-vmstate: define a vmstate entry for clock state

hw/core/clock-vmstate: define a vmstate entry for clock state

Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 20200406135251.157596-3-damien.hedde@greensocs.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>