blackfin: fix building error by adding macro CONFIG_SYS_I2C

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
diff --git a/include/configs/bf561-ezkit.h b/include/configs/bf561-ezkit.h
index 404039a..fb6f948 100644
--- a/include/configs/bf561-ezkit.h
+++ b/include/configs/bf561-ezkit.h
@@ -90,6 +90,7 @@
  */
 #define CONFIG_SYS_I2C_SOFT
 #ifdef CONFIG_SYS_I2C_SOFT
+#define CONFIG_SYS_I2C
 #define CONFIG_SOFT_I2C_GPIO_SCL GPIO_PF0
 #define CONFIG_SOFT_I2C_GPIO_SDA GPIO_PF1
 #define I2C_DELAY		udelay(5)	/* 1/4 I2C clock duration */