basic multi-plane support

[illegalprime]

I care about creating a capture stream with a multi-plane camera. I have a basic version of it working, with inspiration from your mplane branch. What works:

1. get/set/list formats
2. create an mmap capture stream
3. stream frames from it

[tepperson2]

I would like to see this merged into a release as I am also interested in using this on an imx8 system.

[MarijnS95]

Nit: there's a matches!(self, Type::VideoCaptureMplane | Type::VideoOutputMplane) macro for this:

Suggested change

	match self {
	Type::VideoCaptureMplane | Type::VideoOutputMplane => true,
	_ => false,
	}
	matches!(self, Type::VideoCaptureMplane | Type::VideoOutputMplane)

[anatawa12]

When I tried to use this branch for my application, which use both multi plane and single plane, I received error with single plane device. This fix works with my environment.

Suggested change

	let ptr = v4l2::mmap(
	ptr::null_mut(),
	plane.length as usize,
	libc::PROT_READ | libc::PROT_WRITE,
	libc::MAP_SHARED,
	self.handle.fd(),
	plane.m.mem_offset as libc::off_t,
	)?;
	planes.push(slice::from_raw_parts_mut::<u8>(
	ptr as *mut u8, plane.length as usize
	));
	let length = if !self.buf_type.planar() { v4l2_buf.length as usize } else { plane.length as usize };
	let ptr = v4l2::mmap(
	ptr::null_mut(),
	length,
	libc::PROT_READ | libc::PROT_WRITE,
	libc::MAP_SHARED,
	self.handle.fd(),
	plane.m.mem_offset as libc::off_t,
	)?;
	planes.push(slice::from_raw_parts_mut::<u8>(
	ptr as *mut u8, length,
	));

[Type1J]

@raymanfx, @illegalprime, and @anatawa12 I have a project that uses a single plane, and a plan to add support for a multiple plane device. This PR only introduced only 1 breaking change (this project is still in 0 major, so that shouldn't be an issue) to my project, which is that Stream::next() gives a slice of slices instead of a slice. The type system will give the user information about what needs changing, and the Cargo.lock file will prevent the change from occurring for people who just want to make a working build of something, and don't want to fix anything to work with newer libs at the moment, so this PR can be merged as soon as illegalprime#1 lands. Thanks!

[illegalprime]

Thank you for cleaning up the conflicts! Even though nobody's experience would necessarily break with this addition it should still not be merged until the author decides this is the abstraction they prefer.