* Add CMake module for building CHIP examples with Nordic NCS

Currently Nordic platform layer of CHIP is based on nRF5
SDK. This commit is the first step needed to replace it
with nRF Connect SDK based on Zephyr RTOS. While the old
platform layer remains unchanged, add a CMake helper file
which allows to build the entire CHIP using the NCS/Zephyr
build system.

* Port part of the door-lock example to Nordic Connect SDK

Rewrite everything which doesn't depend on the CHIP platform
layers using the NCS/Zephyr API. This includes functionality
of the sample app related to LEDs, buttons, timers, message
queues and logging.

* Implement PlatformManagerImpl for nRF Connect SDK

Implement PlatformManagerImpl for nRF Connect SDK based on
generic implementation for Zephyr RTOS. Also provide initial
implementation of functions to retrieve system time using
Zephyr API and add Zephyr-based logging backend.

The code compiles, but it requires other components to be
tested.

* Add empty stubs for nRF Connect platform layer

This commit adds empty implementations of base platform functions.

* Add ThreadStackManager implementation and enable OT

This commit enables the OT stack in the Zephyr application.
The ThreadStackManager allows the CHIP stack to control the
state of the stack embedded into the Zephyr.
It is required that all calls to this class are to be made
from a cooperative task priority.

* Adapt Inet layer to Zephyr networking API

Make necessary changes to build CHIP Inet library using
Zephyr networking API. Zephyr provides BSD-like socket
interface, however a few things are missing:

- some socket-related functions are not available, e.g.
  getsockname, recvmsg etc. Implement required
  replacements.
- some constants are not available. In particular, some
  options passed to the setsockopt function must have been
  made optional. In case e.g. explicit multicast group
  management is needed we will have find another ways
  to implement that in Zephyr.
- the whole ifaddrs library doesn't exist in Zephyr, so
  all the interface/address enumeration code must have been
  implemented for Zephyr.
- disable TCP end point for nRF Connect SDK platform for
  now as it will require further changes.

* Add ConnectivityManager for nRF Connect

* Add README.md

* Add ZCL server to the door-lock example for nRF Connect

Co-authored-by: Rafał Kuźnia <rafal.kuznia@nordicsemi.no>

* Apply code-review suggestions

* Restyled by whitespace

Co-authored-by: Rafał Kuźnia <rafal.kuznia@nordicsemi.no>
Co-authored-by: Restyled.io <commits@restyled.io>