[nrf fromlist] drivers: timer: nrf_grtc_timer: Add system_clock_disable implementation

Add implementation of `sys_clock_disable` function for GRTC timer.

Upstream PR #: 99305

Signed-off-by: Adam Kondraciuk <adam.kondraciuk@nordicsemi.no>

Author: adamkondraciuk

drivers/timer/nrf_grtc_timer.c

@@ -366,6 +366,10 @@ uint64_t z_nrf_grtc_timer_startup_value_get(void)
 #if defined(CONFIG_POWEROFF) && defined(CONFIG_NRF_GRTC_START_SYSCOUNTER)
 int z_nrf_grtc_wakeup_prepare(uint64_t wake_time_us)
 {
+	if (!nrfx_grtc_init_check()) {
+		return -ENOTSUP;
+	}
+
 	nrfx_err_t err_code;
 	static uint8_t systemoff_channel;
 	uint64_t now = counter();
@@ -463,6 +467,21 @@ ISR_DIRECT_DECLARE(nrfx_grtc_direct_irq_handler)
 }
 #endif
 
+void sys_clock_disable(void)
+{
+	nrfx_grtc_uninit();
+#if defined(CONFIG_CLOCK_CONTROL_NRF)
+	int err;
+	struct onoff_manager *mgr =
+		z_nrf_clock_control_get_onoff((clock_control_subsys_t)CLOCK_CONTROL_NRF_TYPE_LFCLK);
+
+	err = onoff_release(mgr);
+	__ASSERT_NO_MSG(err >= 0);
+
+	nrfx_coredep_delay_us(1000);
+#endif
+}
+
 static int sys_clock_driver_init(void)
 {
 	nrfx_err_t err_code;