Blackfin: bf518f-ezbrd: enable SST SPI flash driver

The BF51xF parts have an internal SST SPI flash, so make sure the driver is
enabled by default so we can access it.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

include/configs/bf518f-ezbrd.h

@@ -90,6 +90,7 @@
 #define CONFIG_ENV_SPI_MAX_HZ	30000000
 #define CONFIG_SF_DEFAULT_HZ	30000000
 #define CONFIG_SPI_FLASH
+#define CONFIG_SPI_FLASH_SST
 #define CONFIG_SPI_FLASH_STMICRO