Split GPIO registers into named bit fields

[MabezDev]

Would be nice to have a nicer api instead of manually bit shifting, e.g

Replace

gpio_reg_x.write(|w| unsafe { w.bits(0x1 << 0) });

With, or similar

gpio_reg_x.write(|w| w.gpio0().set_bit())

[davidkern]

Hey thanks for getting an SVD up yesterday. I was in progress of building out a register set for the ESP32, but have stopped in preference to using this.

Is the work for this ticket still required to split out the registers into individual fields? I can work on it if needed.

[MabezDev]

@davidkern that would be great!