dfu: add dependency on the raw NAND core

CONFIG_DFU_NAND needs the raw NAND core being compiled.

Also fix the colibri_vf defconfig to reflect this dependency.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
diff --git a/drivers/dfu/Kconfig b/drivers/dfu/Kconfig
index 02bc28f..75fe0a1 100644
--- a/drivers/dfu/Kconfig
+++ b/drivers/dfu/Kconfig
@@ -31,6 +31,7 @@
 config DFU_NAND
 	bool "NAND back end for DFU"
 	depends on CMD_MTDPARTS
+	depends on MTD_RAW_NAND
 	help
 	  This option enables using DFU to read and write to NAND based
 	  storage.