Remove littlefs2 macros

[robin-nitrokey]

• littlefs2_prince_filesystem always enables the entire PRINCE region 2 which can be problematic if this region is not used exclusively for the filesystem. It is hard to provide a correct and general implementation so I would transform this macro into an example that can be adapted depending on the use case.
  

  lpc55-hal/src/drivers/flash.rs

  Lines 527 to 532 in 53a86f7

  	self.prince.enable_region_2_for(||{
  	let flash: *const u8 = (Self::BASE_OFFSET + off) as *const u8;
  	for i in 0 .. buf.len() {
  	buf[i] = unsafe{ *flash.offset(i as isize) };
  	}
  	});

• littlefs2_filesystem could just be a struct using const generics.
  

  lpc55-hal/src/drivers/flash.rs

  Line 395 in 53a86f7

  macro_rules! littlefs2_filesystem {