clock: Add ClockEvent parameter to callbacks

The Clock framework allows users to specify a callback which is
called after the clock's period has been updated.  Some users need to
also have a callback which is called before the clock period is
updated.

As the first step in adding support for notifying Clock users on
pre-update events, add an argument to the ClockCallback to specify
what event is being notified, and add an argument to the various
functions for registering a callback to specify which events are
of interest to that callback.

Note that the documentation update renders correct the previously
incorrect claim in 'Adding a new clock' that callbacks "will be
explained in a following section".

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Luc Michel <luc@lmichel.fr>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210219144617.4782-2-peter.maydell@linaro.org

hw/watchdog/cmsdk-apb-watchdog.c

@@ -310,7 +310,7 @@ static void cmsdk_apb_watchdog_reset(DeviceState *dev)
     ptimer_transaction_commit(s->timer);
 }
 
-static void cmsdk_apb_watchdog_clk_update(void *opaque)
+static void cmsdk_apb_watchdog_clk_update(void *opaque, ClockEvent event)
 {
     CMSDKAPBWatchdog *s = CMSDK_APB_WATCHDOG(opaque);
 
@@ -329,7 +329,8 @@ static void cmsdk_apb_watchdog_init(Object *obj)
     sysbus_init_mmio(sbd, &s->iomem);
     sysbus_init_irq(sbd, &s->wdogint);
     s->wdogclk = qdev_init_clock_in(DEVICE(s), "WDOGCLK",
-                                    cmsdk_apb_watchdog_clk_update, s);
+                                    cmsdk_apb_watchdog_clk_update, s,
+                                    ClockUpdate);
 
     s->is_luminary = false;
     s->id = cmsdk_apb_watchdog_id;