arm: Add support for Nordic Semiconductor's nRF52 series of ICs

Add SoC support for the Nordic Semiconductor nRF52 series.

JIRA: ZEP-377
Change-Id: Idb476f43d7ca35f87c73910dd9bd1c50032ccdbe
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>