hw/timer: Refactor NPCM7XX Timer to use CLK clock

This patch makes NPCM7XX Timer to use a the timer clock generated by the
CLK module instead of the magic number TIMER_REF_HZ.

Reviewed-by: Havard Skinnemoen <hskinnemoen@google.com>
Reviewed-by: Tyrone Ting <kfting@nuvoton.com>
Signed-off-by: Hao Wu <wuhaotsh@google.com>
Message-id: 20210108190945.949196-3-wuhaotsh@google.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

include/hw/timer/npcm7xx_timer.h

@@ -101,6 +101,7 @@ struct NPCM7xxTimerCtrlState {
 
     uint32_t    tisr;
 
+    Clock       *clock;
     NPCM7xxTimer timer[NPCM7XX_TIMERS_PER_CTRL];
     NPCM7xxWatchdogTimer watchdog_timer;
 };