drivers: prepare for moving EEPROM definitions

IMHO and I think it's more logical, EEPROM definitions don't belong
to cpu_conf.h but to periph_conf.h, thus I moved all of them to that
place.

drivers/periph_common/eeprom.c

@@ -19,7 +19,9 @@
  */
 
 #include <string.h>
+
 #include "cpu.h"
+#include "periph_cpu.h"
 #include "assert.h"
 
 /* guard this file, must be done before including periph/eeprom.h */