Refactor devicetree parsing and driver interface

Ideally, we would let the drivers handle most of the devicetree parsing and keep a mapping of compatibles to drivers so that we can probe all the drivers for the devicetree in use.

We should however abstract away more of the low-level parsing (i.e. expose the defined interrupts and memory regions with a higher-level interface).

A driver would then e.g. define a `probe` method that takes the devicetree node it was matched on as a parameter. It would then set up interrupt handlers, configure GPIOs, etc.