nios: config: Update neek defconfig

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
nios2: Support per-name dtb builds

Let's add support for 'make foo.dtb', just as the ARM world is doing.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
nios2: boot: Move devicetree files to their new home

Move the devicetree source files to arch/${ARCH}/boot/dts,
and behave like all the other architectures. This way, we'll
stop feeling lonely.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>