Flag EEPROM write errors on serial output

- Also adds a language string for the error.
- Also adds SERIAL_EOL as an alias for SERIAL_ECHOLN(“”)

Marlin/Marlin.h

@@ -86,6 +86,8 @@ extern const char echomagic[] PROGMEM;
 
 #define SERIAL_ECHOPAIR(name,value) (serial_echopair_P(PSTR(name),(value)))
 
+#define SERIAL_EOL SERIAL_ECHOLN("")
+
 void serial_echopair_P(const char *s_P, float v);
 void serial_echopair_P(const char *s_P, double v);
 void serial_echopair_P(const char *s_P, unsigned long v);