Add instances for Solo (GHC-9.0 and 9.2)

[phadej]

cc @treeowl

[treeowl]

Yes. I still don't have solid word on whether it'll be in base in 9.2, but it's already in ghc-prim.

[phadej]

It would be great if deepseq bundled with GHC-9.2 had instances already (depending on ghc-prim shouldn't be a problem).

Ping @sjakobi

[sjakobi]

@phadej I assume you pinged me believing that I'm a a maintainer for deepseq. I'm not though. All my commits to deepseq were merged by @chessai, who is the only active deepseq maintainer I'm aware of.

[chessai]

I would take a PR for this. @treeowl we can just depend on ghc-prim without issue, if Solo won't be in base in 9.2. cc @bgamari for whether or not that's the case