Add an RP2350 HAL.

[thejpster]

Taken from https://github.com/thejpster/rp-hal-rp2350-public, with minor tweaks.

[thejpster]

Hey, it finally completed all 98 jobs!

[thejpster]

OK I think I hit them all. RIP all those GHA free minutes.

[jannic]

Some files got updates for rp2040 after you did the copy for rp235x.
Two examples I found were #831 for SPI and #798 for UART.
We could either update the pull request, or merge it first and then check for unintended divergences. What would you prefer?
(Maybe we can also do some more code deduplication?)

[9names]

We could either update the pull request, or merge it first and then check for unintended divergences.

Lets do it the latter way, it would be better as smaller update PRs.
Github really struggled when I was trying to review this mega PR, the sooner it's closed the better.

[9names]

LGTM, couple of copy-paste errors on datasheet URL but otherwise good to go

[thejpster]

Maybe we can also do some more code deduplication?

Yes, once this is in there's a lot of scope for de-duplication. I wasn't able to track the rp2040-hal whilst working in my private repo, so it sort of diverged. Then to open this PR I had to rebase a bunch of stuff and try and get closer to where you were (but you kept moving). I propose that after this goes in we do a diff -r rp2040-hal rp235x-hal and try and remove as many diffs as possible - either with changes to one of the HALs, or by moving things into rp-common-hal.