ext: Import Nordic SDK HAL files

Nordic Semiconductor's Software Development Kit's HAL layer
provides a set of low-level header and sourcefiles that give access to
the different hardware peripherals of Nordic ICs.

Origin: Nordic SDK 12.2.0 (components/drivers_nrf/hal)
URL: http://developer.nordicsemi.com/nRF5_SDK/


License: 3-clause BSD
Maintained-by: External

Change-Id: Iafb5816af89461c8e88ba3b47e790cb6141d10fe
Signed-off-by: Wojciech Bober <wojciech.bober@nordicsemi.no>
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>