Move package imports to module scope

[meggiman]

Import packages into the compilation unit scope (meaning you put the import before the module declaration) is very bad practice. Depending on the tool (whether it puts every file into one single compilation unit or every file in its own compilation unit), it causes imported symbols with identical name to be overriden. E.g. this module's .* imports clash with the imports in the hwpe-mac-engine IP. Instead the import should happen after the module name declaration before the parameter list. That way, the import is scoped to the module.