drivers/spi: Sanitize headers from preprocessor abuse

Continuing on from the rational given in:

a173a62 Remove guarding #includes by CONFIG_FOO combinations

Change-Id: I35c636ee7c0b106323b3e4b90629f7262750f8bd
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/6114
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/drivers/spi/spi_flash_internal.h

@@ -4,6 +4,9 @@
  * Copyright (C) 2008 Atmel Corporation
  */
 
+#ifndef SPI_FLASH_INTERNAL_H
+#define SPI_FLASH_INTERNAL_H
+
 /* Common parameters -- kind of high, but they should only occur when there
  * is a problem (and well your system already is broken), so err on the side
  * of caution in case we're dealing with slower SPI buses and/or processors.
@@ -83,3 +86,5 @@ struct spi_flash *spi_flash_probe_gigadevice(struct spi_slave *spi,
 					     u8 *idcode);
 struct spi_flash *spi_flash_probe_adesto(struct spi_slave *spi, u8 *idcode);
 struct spi_flash *spi_fram_probe_ramtron(struct spi_slave *spi, u8 *idcode);
+
+#endif /* SPI_FLASH_INTERNAL_H */