[nrf fromtree] tests: nrf: enable twister tests for nrf54l20pdk

Enabled the following tests on nrf54l20
- i2c_slave
- clock_control_api
- nrf_clock_calibration
- nrf_lf_clock_start
- onoff
- retained_mem/api
- uart_elementary
- uart_errors
- uart_mix_fifo_poll
- uart_pm
- uart_async_api
- wdt_error_cases
- wdt_basic_api
- counter_basic_api
- fcb
- nrf/qdec

Signed-off-by: Rafał Kuźnia <[email protected]>
(cherry picked from commit 07ee796)

Signed-off-by: Sebastian Głąb <[email protected]>

tests/drivers/watchdog/wdt_error_cases/src/main.c

@@ -42,8 +42,12 @@
 #define DEFAULT_WINDOW_MIN (0U)
 
 /* Align tests to the specific target: */
+<<<<<<< HEAD
 #if defined(CONFIG_SOC_SERIES_NRF54LX) || defined(CONFIG_SOC_NRF54H20) || \
 	defined(CONFIG_SOC_NRF9280)
+=======
+#if defined(CONFIG_SOC_SERIES_NRF54LX) || defined(CONFIG_SOC_NRF9280)
+>>>>>>> [nrf fromtree] tests: nrf: enable twister tests for nrf54l20pdk
 #define WDT_TEST_FLAGS                                                                             \
 	(WDT_DISABLE_SUPPORTED | WDT_FLAG_RESET_SOC_SUPPORTED |                                    \
 	 WDT_FLAG_ONLY_ONE_TIMEOUT_VALUE_SUPPORTED | WDT_OPT_PAUSE_IN_SLEEP_SUPPORTED |            \