542: nrf/gpiote: remove PortInput, move impls to Input/FlexPin. r=Dirbaio a=Dirbaio
`PortInput` is just a dumb wrapper around `Input`, it has no reason whatsoever to exist. This PR moves the `wait_for_x` functionality to `Input` directly.
It also adds it to `FlexPin` for completeness and consistency with `Input`.
(The reason `PortInput` exists is a while ago `GPIOTE` was an owned singleton that you had to initialize, so `PortInput::new()` would require it to enforce it's been initialized. This doesn't apply anymore now that GPIOTE is "global")
Co-authored-by: Dario Nieuwenhuis <dirbaio@dirbaio.net>
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