dm: sandbox: Move driver model CONFIGs to Kconfig

Remove driver model CONFIGs from the board config headers and use Kconfig
instead.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/sandbox/Kconfig

@@ -10,4 +10,28 @@ config SYS_BOARD
 config SYS_CONFIG_NAME
 	default "sandbox"
 
+config DM
+	default y
+
+config DM_GPIO
+	default y
+
+config DM_SERIAL
+	default y
+
+config DM_CROS_EC
+	default y
+
+config DM_SPI
+	default y
+
+config DM_SPI_FLASH
+	default y
+
+config DM_I2C
+	default y
+
+config DM_TEST
+	default y
+
 endmenu