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/MPC8544DS_defconfig b/configs/MPC8544DS_defconfig
index aef9bac..cb15afa 100644
--- a/configs/MPC8544DS_defconfig
+++ b/configs/MPC8544DS_defconfig
@@ -15,6 +15,7 @@
 CONFIG_CMD_PING=y
 # CONFIG_CMD_HASH is not set
 CONFIG_CMD_EXT2=y
+CONFIG_SCSI=y
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_NETDEVICES=y