Some code in OpenTitan uses "import" at top-level in a class

[rswarbrick]

Description

This isn't allowed (see footnote 11 in section A.10 of the 1800 spec). It turns out that many EDA tools don't mind, which is why we hadn't noticed. But Questa generates an error.

I believe that there are just two instances of this, with potential examples found by searching for files that contain "class" and an "import" line:

git grep -l 'import ' '*.sv' >with-import.lst
grep <with-import.lst -v autogen | xargs grep -l '^\s*class' | sort -u >both.lst

There were 26 hits and I think two genuine examples.