boards: Add support for the nRF52 DK board (PCA10040)

Add board support for the Nordic Semiconductor's
nRF52832 (nRF52 series) Development Kit.

JIRA: ZEP-377
Change-Id: I6d8f1f7ec1b8a068193f6ba67c8a1ab9f399f80b
Signed-off-by: Glenn Ruben Bakke <glenn.ruben.bakke@nordicsemi.no>
Signed-off-by: Vinayak Kariappa Chettimada <vinayak.kariappa.chettimada@nordicsemi.no>
Signed-off-by: Håkon Alseth <haakon.alseth@nordicsemi.no>
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>