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/board/dfi/Kconfig b/board/dfi/Kconfig
index 25d0a11..d2a1d78 100644
--- a/board/dfi/Kconfig
+++ b/board/dfi/Kconfig
@@ -12,6 +12,7 @@
 
 config TARGET_DFI_BT700
 	bool "DFI BT700 BayTrail"
+	imply SCSI
 	help
 	  This is the DFI Q7X-151 baseboard equipped with the
 	  DFI BayTrail Bt700 SoM. It contains an Atom E3845 with