variants: create giga_m7 variant

Author: facchinm

variants/arduino_giga_r1_m7/variant.cpp

@@ -0,0 +1,8 @@
+#include <zephyr/kernel.h>
+
+void _on_1200_bps() {
+    uint32_t tmp = (uint32_t) & (RTC->BKP0R);
+    tmp += (RTC_BKP_DR0 * 4U);
+    *(__IO uint32_t *)tmp = (uint32_t)0xDF59;
+    NVIC_SystemReset();
+}

variants/arduino_giga_r1_m7/variant.h

@@ -0,0 +1,13 @@
+/*
+ * Copyright (c) 2022 Dhruva Gole
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+// TODO: correctly handle these legacy defines
+#define MOSI    0
+#define MISO    0
+#define SCK     0
+#define SS      0
+#define SDA     0
+#define SCL     0