Convert CONFIG_SCSI to Kconfig

This converts the following to Kconfig:
   CONFIG_SCSI

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/configs/Cubietruck_defconfig b/configs/Cubietruck_defconfig
index f9d56c8..cbd535c 100644
--- a/configs/Cubietruck_defconfig
+++ b/configs/Cubietruck_defconfig
@@ -22,6 +22,7 @@
 # CONFIG_SPL_DOS_PARTITION is not set
 # CONFIG_SPL_ISO_PARTITION is not set
 # CONFIG_SPL_PARTITION_UUIDS is not set
+CONFIG_SCSI=y
 CONFIG_DFU_RAM=y
 CONFIG_ETH_DESIGNWARE=y
 CONFIG_RGMII=y