Provide an overidable nop default for BOARD_EEPROM_WP_CTRL

To simplify integration of an EEPROM device with a Write Protect
  control pin, we add an overidable BOARD_EEPROM_WP_CTRL macro
  the does nothing.

  A board that provids the GPIO for WP should define
  BOARD_EEPROM_WP_CTRL(_protected_true) that will set the WP GPIO
  to the Protected state when passed true.

src/drivers/boards/common/board_common.h

@@ -92,6 +92,12 @@
 #define PX4_SPI_BUS_ID(bd)        (((bd) >> 4) & 0xf)
 #define PX4_SPI_DEV_ID(bd)        ((bd) & 0xf)
 
+/* Provide an overridable default nop
+ * for BOARD_EEPROM_WP_CTRL
+ */
+#if !defined(BOARD_EEPROM_WP_CTRL)
+#  define BOARD_EEPROM_WP_CTRL(on_true)
+#endif
 /************************************************************************************
  * Private Functions
  ************************************************************************************/