add a lot of register derives + serde support for cortex-ar

[robamu]

No description provided.

[jonathanpallant]

What's the use-case for sending copies of processor registers through serde?

[robamu]

I commonly add those derives for most types. It might possibly be interesting for error related registers (DFSR and IFSR) or registers like CPSR. In the end, I thought, why not add them for every register then, and added it to all registers using sd. I suppose it is not a common use-case though. Cortex-M has serde support, but only for the SCB (https://github.com/rust-embedded/cortex-m/blob/master/cortex-m/src/peripheral/scb.rs). Does not cost much though (serde is not added by default) and might possibly be useful.