ext: hal: nordic: Add nrfx_config for nRF9160 SoC

Add the header file with the nrfx drivers configuration suitable for
the nRF9160 SoC. This file contains also definitions of CMSIS symbols
(like NRF_CLOCK or NRF_SPIM0) for structures of peripheral registers.
These symbols are used in nrfx HALs and drivers, and for other nRF SoCs
they come from MDK files. For nRF9160 they need to be mapped to proper
addresses in Secure or Non-Secure domain, so we use the information
coming from DT to get it done automatically.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>