DMA: check Align512 struct

[sosthene-nitrokey]

lpc55-hal/src/peripherals/dma.rs

Line 17 in 53a86f7

struct Align512(

I'm not sure I understand the need for this alignment (its not documented in the unsafe blocks), and more importantly, I don't understand the need for the multiple descriptors when there is the #[repr(align(512))]