dm: sandbox: spi: Move to driver model

Adjust the sandbox SPI driver to support driver model and move sandbox over
to driver model for SPI.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>
diff --git a/include/configs/sandbox.h b/include/configs/sandbox.h
index 022629f..8b74f49 100644
--- a/include/configs/sandbox.h
+++ b/include/configs/sandbox.h
@@ -97,8 +97,7 @@
 #define CONFIG_CMD_SF_TEST
 #define CONFIG_CMD_SPI
 #define CONFIG_SPI_FLASH
-#define CONFIG_OF_SPI
-#define CONFIG_OF_SPI_FLASH
+#define CONFIG_DM_SPI
 #define CONFIG_SPI_FLASH_ATMEL
 #define CONFIG_SPI_FLASH_EON
 #define CONFIG_SPI_FLASH_GIGADEVICE