*LPC546XX: Finish MCU Refactoring
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### Description
The Mbed 2 release was broken for FF_LPC546XX as it would include
the entire mbed 2 build of the LPC546XX. This PR seperates these 2
builds completely by:
* Removing non-shared extra labels from the MCU_LPC546XX target
* Moving the target implementation to a shared target directory
### Pull request type
[x] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Breaking change
Jimmy Brisson
committed
on 19 Nov 2018