dra7xx-evm.conf: re-enable dra71-evm-nand.dtb again
dra7xx-evm.conf: re-enable dra71-evm-nand.dtb again

This reverts commit c2cb48e3020459c6d426a13a7180ed26742c1579.

Signed-off-by: Denys Dmytriyenko <d29de71aea38aad3a87d486929cb0aad173ae612@ti.com>

rcn-ee/meta-ti,rcn-ee/meta-ti,rcn-ee/meta-ti,rcn-ee/meta-ti