arm: dts: nrf: Remove !HAS_DTS Kconfig bits

Now that all the nRF based board/SoCs have device trees, we can remove
the Kconfig bits that are now coming from device tree.

Change-Id: Ia1a870a50582d4109070d2833660f58fd6f8691f
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>