Decrease compile time with nanostack-libservice

[ccli8]

Summary of changes

nanostack-libservice involves two parts: common (e.g. libip4string) and nanostack-specific (e.g. nvmHelper). For nanostack-specific, it needs to link nanostack hal and will pull in 200+ nanostack files for compile. This is unnecessary for common only application e.g. lwipstack. To fix this, the following strategy is applied for nanostack-libservice cmake listfile:

1. For compiling nanostack-specific, it doesn't rely on nanostack hal because its needed header file has placed underneath (mbed-client-libservice/platform).
2. For application needing the nanostack-specific, the nanostack cmake listfile shall specify the link dependency.

This actually rolls back #378 on this line

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Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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[multiplemonomials]

Ah yeah. I believe I added this dependency because mbed-nanostack-libservice contains arm_hal_interrupt.h, but the corresponding functions are actually implemented in arm_hal_interrupt.c which is part of mbed-nanostack-hal_mbed_cmsis_rtos. So, you get an undefined reference if you just use those functions without also linking mbed-nanostack-hal_mbed_cmsis_rtos, which feels gross. But still, you're right that this pulls in a large dependency which I did not mean to do -- nice catch! Since it built OK, I am alright to merge this for now, though I still wonder if there's a better way to set this up.