drivers: serial: nrfx_uarte: set/clear pins retention

When GPD is managed by pinctrl, pins retention needs to be controlled by
the driver to avoid glitches.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>

drivers/serial/uart_nrfx_uarte.c

@@ -23,6 +23,11 @@
 #include <zephyr/linker/devicetree_regions.h>
 #include <zephyr/irq.h>
 #include <zephyr/logging/log.h>
+
+#ifdef CONFIG_SOC_NRF54H20_GPD
+#include <nrf/gpd.h>
+#endif
+
 LOG_MODULE_REGISTER(uart_nrfx_uarte, CONFIG_UART_LOG_LEVEL);
 
 #if !defined(CONFIG_ARCH_POSIX)
@@ -2098,6 +2103,9 @@ static void uarte_pm_resume(const struct device *dev)
 
 	if (IS_ENABLED(CONFIG_PM_DEVICE_RUNTIME) || !LOW_POWER_ENABLED(cfg)) {
 		uarte_periph_enable(dev);
+#ifdef CONFIG_SOC_NRF54H20_GPD
+		nrf_gpd_retain_pins_set(cfg->pcfg, false);
+#endif
 	}
 }
 
@@ -2160,6 +2168,10 @@ static void uarte_pm_suspend(const struct device *dev)
 		wait_for_tx_stopped(dev);
 	}
 
+#ifdef CONFIG_SOC_NRF54H20_GPD
+	nrf_gpd_retain_pins_set(cfg->pcfg, true);
+#endif
+
 	nrf_uarte_disable(uarte);
 
 	(void)pinctrl_apply_state(cfg->pcfg, PINCTRL_STATE_SLEEP);