Simplify top scripts (continuation of PR #101)

[tcal-x]

Continuation of PR #101.

Updated VexRiscv verilogs to remove wrappers and not rename the VexRiscv core with "_inner".

Small updates to the handling of Slim VexRiscv -- they can still use the new CFU integration,
their source just needs to be changed.

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[tcal-x]

@robertszczepanski we will close PR #101, and your commits will be merged with this PR, which also contains the necessary VexRiscv updates. Please check the Googlebot (google-cla) comment above.

[robertszczepanski]

@googlebot I consent.