Add NS_DUMMY_DEFINITIONS_OK

[SeppoTakalo]

Add definition from master repository.
This fixes compilation of coap_service.c on non-secure platforms.

Description

Currently, any application requiring FEATURE_NANOSTACK and FEATURE_COMMON_PAL fails to build.
Apparently when Coap-service was updated, it pulls in a code that uses macro NS_DUMMY_DEFINITIONS_OK that is in the master repository of libservice, but not on the version in mbed-OS tree.

Status

READY

Steps to test or reproduce

1. Clone mbed-os-example-blinky
2. Set target without HW entropy, like NUCLEO_F401RE
3. Add features NANOSTACK and COMMON_PAL into mbed_app.json
   Fails to compile.

[SeppoTakalo]

@0xc0170 @sg- We need this in quite quickly in order to be ready for 5.4 code freeze.

Apparently, we don't build Mesh examples to unsecure platforms, when verifying PRs.
This code that triggered the build error is after condition that when mbed TLS is not available.
Therefore it was not visible for most of our platforms.

[sg-]

/morph test

[mbed-bot]

Result: SUCCESS

Your command has finished executing! Here's what you wrote!

/morph test

Output

mbed Build Number: 1692

All builds and test passed!