tests/periph: add test-application for peripheral freqm

tests/periph/freqm/Makefile

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+BOARD ?= same54-xpro
+
+include ../Makefile.periph_common
+
+USEMODULE += periph_freqm
+
+include $(RIOTBASE)/Makefile.include

tests/periph/freqm/README.md

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+Peripheral FREQM Test Application
+=====================================
+
+This application tests the frequency meter (FREQM) functionality. This is done
+by measuring the frequency of a clock, connected to a GPIO, with an internal
+clock as reference.
+
+Expected Output on Success
+--------------------------
+
+    main(): This is RIOT! (Version: <INSERT VERSION HERE>)
+    FREQM peripheral driver test
+    Measured clock frequency: <MEASURED CLOCK FREQUENCY> Hz
+    Test run finished.

tests/periph/freqm/main.c

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+/*
+ * Copyright (C) 2023 ML!PA Consulting GmbH
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     tests
+ * @{
+ *
+ * @file
+ * @brief       Application to test functionality of the frequency meter
+ *              peripheral
+ *
+ * @author      Urs Gompper <urs.gompper@ml-pa.com>
+ * @}
+ */
+
+#include <stddef.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+
+#include "periph/freqm.h"
+
+int main(void)
+{
+    puts("FREQM peripheral driver test");
+
+    /* Initialize frequency meter peripheral */
+    freqm_init(0);
+
+    uint32_t period_us = UINT32_MAX;
+    uint32_t freq_hz = 0;
+
+    /* Measure in blocking mode */
+    if (!freqm_frequency_get(0, &freq_hz, period_us)) {
+        printf("Measured Clock Frequency: %ld Hz\n", freq_hz);
+    }
+    else {
+        puts("Overflow occurred to the FREQM value counter!");
+        return EXIT_FAILURE;
+    }
+
+    puts("Test run finished.");
+
+    /* main thread exits */
+    return 0;
+}