cpu/atmega_common: Drop legacy include

Drop `#include "irq.h"` in `cpu.h`, which was there for a legacy work around.
A bunch of missing includes of `irq.h` materialized due to this and were
fixed.

boards/waspmote-pro/board.c

@@ -24,6 +24,7 @@
 
 #include "board.h"
 #include "cpu.h"
+#include "irq.h"
 
 /**
  * @brief Initialize the boards on-board LEDs (green and red)

cpu/atmega_common/avr_libc_extra/posix_unistd.c

@@ -19,9 +19,10 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
+#include "irq.h"
+
 #ifdef MODULE_VFS
 #include <fcntl.h>
-#include "irq.h"
 #include "vfs.h"
 #elif defined(MODULE_STDIO_UART)
 #include "stdio_uart.h"

cpu/atmega_common/include/cpu.h

@@ -37,11 +37,6 @@
 #include "cpu_conf.h"
 #include "sched.h"
 #include "thread.h"
-/**
- * For downwards compatibility with old RIOT code.
- * TODO: remove once core was adjusted
- */
-#include "irq.h"
 
 #ifdef __cplusplus
 extern "C"

cpu/atmega_common/periph/uart.c

@@ -32,6 +32,7 @@
  */
 
 #include "cpu.h"
+#include "irq.h"
 #include "sched.h"
 #include "thread.h"