Core Params - Allow additional external config

Created by: silabs-robin

This PR lets a "param_set_1" to be externally defined, to test a complement of "param_set_0". @silabs-hfegran

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(Side note: I am actually in favor of removing the "else" clauses of the constants file, because they are pitfalls for when one forgets to set something in a config. I think the elses might be a bigger danger/inconvenience than they are a convenience. But that is a different discussion.)