rp235x-hal: Add nice wrapper for `get_sys_info`

[thejpster]

The get_sys_info ROM function is a grab-bag of stuff. We should have a nice Rust API for each kind of thing it can produce. Probably a separate function for each kind of thing, rather than one function with a complicated API like the ROM provides.

[jannic]

@thejpster: I think this issue was solved with #877, or is there something else you'd like to see?

[thejpster]

No, I think that covers it! I can re-open if I find something.