cpu/atmega_common: use the same cpu_conf for all atmega based boards

Removes redundancy of code since all the boards were defining
the same variables. Moreover, the stack sizes are unified per
architecture, as required.

cpu/atmega1284p/include/cpu_conf.h → cpu/atmega_common/include/cpu_conf.h

 /*
  * Copyright (C) 2014 Freie Universität Berlin, Hinnerk van Bruinehsen
+ *               2017 RWTH Aachen, Josua Arndt
  *               2018 Matthew Blue
  *
  * This file is subject to the terms and conditions of the GNU Lesser
@@ -8,7 +9,7 @@
  */
 
 /**
- * @ingroup         cpu_atmega1284p
+ * @ingroup         cpu_atmega_common
  * @{
  *
  * @file
@@ -16,6 +17,8 @@
  *
  * @author          Hauke Petersen <hauke.petersen@fu-berlin.de>
  * @author          Hinnerk van Bruinehsen <h.v.bruinehsen@fu-berlin.de>
+ * @author          Josua Arndt <jarndt@ias.rwth-aachen.de>
+ * @author          Steffen Robertz <steffen.robertz@rwth-aachen.de>
  * @author          Matthew Blue <matthew.blue.neuro@gmail.com>
  */
 
@@ -28,19 +31,23 @@
 extern "C" {
 #endif
 
+#define THREAD_EXTRA_STACKSIZE_PRINTF    (128)
+
 /**
- * @name Kernel configuration
+ * @name           Kernel configuration
  *
- * Since printf seems to get memory allocated by the linker/avr-libc the stack
- * size tested successfully even with pretty small stacks.k
+ *                 Since printf seems to get memory allocated by the
+ *                 linker/avr-libc the stack size tested successfully
+ *                 even with pretty small stacks.
  * @{
  */
-#define THREAD_EXTRA_STACKSIZE_PRINTF    (128)
-
 #ifndef THREAD_STACKSIZE_DEFAULT
-#define THREAD_STACKSIZE_DEFAULT   (256)
+#define THREAD_STACKSIZE_DEFAULT   (512)
 #endif
 
+/* keep THREAD_STACKSIZE_IDLE > THREAD_EXTRA_STACKSIZE_PRINTF
+ * to avoid not printing of debug in interrupts
+ */
 #define THREAD_STACKSIZE_IDLE      (128)
 /** @} */
 
@@ -48,5 +55,6 @@ extern "C" {
 }
 #endif
 
+
 #endif /* CPU_CONF_H */
 /** @} */