Re-add call to suspend_power_down_kb().

In #14210, all previous calls to `suspend_power_down_kb()` were replaced
with calls to `suspend_power_down_quantum()`, together with some much
needed deduplication. However, the `_kb` function was never called from
the `_quantum` one (unlike `suspend_wakeup_init_kb()`).

I followed the example of how it was implemented for AVR before #14210,
i.e. called before the rest of the suspend functions, regardless of the
`NO_SUSPEND_POWER_DOWN` setting.

Fixes #16279.

quantum/quantum.c

@@ -488,6 +488,7 @@ __attribute__((weak)) void suspend_power_down_user(void) {}
 __attribute__((weak)) void suspend_power_down_kb(void) { suspend_power_down_user(); }
 
 void suspend_power_down_quantum(void) {
+    suspend_power_down_kb();
 #ifndef NO_SUSPEND_POWER_DOWN
 // Turn off backlight
 #    ifdef BACKLIGHT_ENABLE