[Target] Add Target Parser for Arm(R) Cortex(R) M-Profile CPUs

[Mousius]

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This implements an initial Target Parser which uses the same logic as the CMSIS-NN compiler flags to update the features and keys of the c and llvm Targets.

Refactoring of the CMSIS-NN logic will be in a separate patch.

[Mousius]

cc @manupa-arm