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/adc/npcm7xx_adc.c

@@ -238,7 +238,7 @@ static void npcm7xx_adc_init(Object *obj)
     memory_region_init_io(&s->iomem, obj, &npcm7xx_adc_ops, s,
                           TYPE_NPCM7XX_ADC, 4 * KiB);
     sysbus_init_mmio(sbd, &s->iomem);
-    s->clock = qdev_init_clock_in(DEVICE(s), "clock", NULL, NULL);
+    s->clock = qdev_init_clock_in(DEVICE(s), "clock", NULL, NULL, 0);
 
     for (i = 0; i < NPCM7XX_ADC_NUM_INPUTS; ++i) {
         object_property_add_uint32_ptr(obj, "adci[*]",