davinci: da850-evm: enable driver model for NAND

Enable the driver-model on da850-evm. We need to add a dummy nand node
to the device tree, as the real nand node is a sub-node of the aemif
device.

On linux the aemif driver populates all its child nodes, but we can't do
it in u-boot currently.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Tested-by: Adam Ford <aford173@gmail.com> #da850-evm
diff --git a/configs/da850evm_defconfig b/configs/da850evm_defconfig
index 99300cb..7de1d2f 100644
--- a/configs/da850evm_defconfig
+++ b/configs/da850evm_defconfig
@@ -52,6 +52,7 @@
 CONFIG_DM_I2C=y
 CONFIG_SYS_I2C_DAVINCI=y
 CONFIG_DM_MMC=y
+CONFIG_MTD=y
 CONFIG_MTD_DEVICE=y
 CONFIG_DM_SPI_FLASH=y
 CONFIG_SPI_FLASH=y