Use atomic register access for RESETS instead of read-modify-write

[ilovefurnaces]

RP2040 Datasheet (2.1.2) states that most peripheral registers can be accessed atomically (bitwise) using offsets: 0 (normal access), 0x1000 (XOR), 0x2000 (bitmask set), 0x3000 (bitmask clear). That allows registers to be accessed concurrently without any synchronization. But currently rp2040-hal uses read-modify-write sequences to RESETS register to reset devices, which is hard to synchronize and is completely unneeded. Atomic accesses should eliminate the need to have &mut RESETS to initialize a peripheral. C pico SDK already uses atomic accesses to hardware registers to do that.

A problem I can see is that rp2040-pac, doesn't support this without pointer arithmetic. But i think that adding convenience functions for that wouldn't be very hard.