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/som-db5800-som-6867_defconfig b/configs/som-db5800-som-6867_defconfig
index ea3d175..56a7e4b 100644
--- a/configs/som-db5800-som-6867_defconfig
+++ b/configs/som-db5800-som-6867_defconfig
@@ -43,6 +43,7 @@
 CONFIG_OF_CONTROL=y
 CONFIG_REGMAP=y
 CONFIG_SYSCON=y
+CONFIG_SCSI=y
 CONFIG_CPU=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_GIGADEVICE=y