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/mips/cps.c

@@ -39,7 +39,7 @@ static void mips_cps_init(Object *obj)
     SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
     MIPSCPSState *s = MIPS_CPS(obj);
 
-    s->clock = qdev_init_clock_in(DEVICE(obj), "clk-in", NULL, NULL);
+    s->clock = qdev_init_clock_in(DEVICE(obj), "clk-in", NULL, NULL, 0);
     /*
      * Cover entire address space as there do not seem to be any
      * constraints for the base address of CPC and GIC.