ARM: davinci: fix DT booting with default defconfig

Davinci boards tend to have older booloaders without DTB support.
Enable appended DTB support by default to allow DT booting on older
platforms.  While there, also enable /proc/device-tree support for
easy verification of DT boot.

Signed-off-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>