[multitop] New bazel rules to describe HW

[pamaury]

The goal of this experiment is to design new rules to better describe the HW and eventually get rid of our current usage of all_files targets. The idea is that each IP contains a new target created by opentitan_ip where the RTL, doc and hjson files are listed. Then, those files targets are collected by an opentitan_top rule that puts together the entire list of doc, RTL and hjson files. One this is done, we start replace all direct usages of HW files by reference to this new top target where we selectively extra only the files we need. Eventually this should apply to:

• all headers (C, rust, multi-top)
• fusesoc
• documentation

More is possible, for example we could point to testplans, we could separate RTL from DV, etc
This change will eventually be needed for multi-top because collecting all files as we currently do will not scale.

Finally, this PR contains another change: instead of pointing to //hw/ip/... for headers, we now collect everything in a new package //hw/top. There are several reasons for that:

• we can start treating all IPs the same way, whether they are in hw/ip or hw/top_/ip/..., autogenerated or not
• this moves us closer to a bazel-configuration-based top selection which will be used for multi-top
• it solves the problem of IPs in hw/top that have top-specifiied parameters but those are not accessible when generating headers the way we currently do.

Since there are many IPs to convert and many files to patch, the approach in this PR is to create a script to automate most of the process. All commits before [util] Add script to convert... are manual. The rest is created automatically by the script to convert IPs and uses one by one, except for the last commit is manual.

Important remark: this does not duplicate any information that fusesoc has, this is completely orthogonal and only use coarse-grained globs to gather all files.

TODO:

• pinmux: if Ipgen pinmux #24808 is merged before, will need to do a few tweaks
• see if we need to handle the node attribute of previous C/rust headers to select the default register node, or if we need to generate several headers for some IPs (one per node)

TODO in follow-up PRs:

• cleanup the OTBN python: it's a complete mess, the way data files are handled and the the way it hack sys.path to point to util/ is not great. I couldn't quite get rid of all_files due to that.