zephyrSerial: Add SPDX Tags and remove unneded includes

This adds SPDX Tags previously not there and also removes headers that
are not really necessary.

Signed-off-by: Dhruva Gole <[email protected]>

Author: DhruvaG2000

cores/arduino/zephyrSerial.cpp

@@ -1,6 +1,10 @@
+/*
+ * Copyright (c) 2022 Dhruva Gole
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 #include <zephyrSerial.h>
-#include <Arduino.h>
-#include <zephyr/sys/printk.h>
 
 size_t arduino::ZephyrSerial::begin(unsigned long int baudrate){
     return 0;

cores/arduino/zephyrSerial.h

@@ -1,7 +1,12 @@
+/*
+ * Copyright (c) 2022 Dhruva Gole
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 #pragma once
 
 #include <Arduino.h>
-#include <api/Print.h>
 
 namespace arduino {