Add support for device path protocol and EFI_LOCATE_DEVICE_PATH

[zdivelbiss]

Motivation

This PR adds support for the EFI_DEVICE_PATH_PROTOCOL, primarily for support with the EFI_LOCATE_DEVICE_PATH function, existing on the EFI_BOOT_SERVICES structure.

Changes

3 new types are added:

#[repr(C)]
#[unsafe_guid("09576e91-6d3f-11d2-8e39-00a0c969723b")]
#[derive(Protocol)]
pub struct DevicePath { /* members elided for brevity */ }

#[repr(u8)]
#[derive(Debug)]
pub enum DeviceType { /* members elided for brevity */ }

#[repr(u8)]
#[derive(Debug)]
pub enum DeviceSubType { /* members elided for brevity */ }

To facilitate usage of these types, and implementing the EFI_LOCATE_DEVICE_PATH function, I added the following function to the Handle struct:

impl Handle {
    pub(crate) unsafe fn uninitialized() -> Self {
        MaybeUninit::zeroed().assume_init()
    }
}

Additionally, I've broken LoadedImage out into its own loaded_image.rs file, for the sake of semantically expanding the types held within the module. The new module format is well expressed by the following:

use uefi::proto::loaded_image::{LoadedImage, DevicePath};

This is obviously not a breaking change, so I felt taking this liberty (given the corollary nature of EFI_DEVICE_PATH_PROTOCOL to EFI_LOADED_IMAGE_PROTOCOL) was acceptable.

The final change is to update the feature optin_builtin_traits to auto_traits, as the feature name has breaking-changed. There already exists a PR for this, but I was unaware of it at the time of the commit.

[GabrielMajeri]

Thanks for the contribution!

I've made a separate PR (#188) which fixed the remaining CI issues, if you rebase (and skip the commit with the unstable feature rename), it should be green.

[zdivelbiss]

I believe (?) I rebased my pull branch, I'm not too familiar with doing PRs (or git in general, to be honest). I'm unsure why the Rust / Lints still fails.

[toku-sa-n]

You can run rustfmt **/*.rs in the repository base directory.

[zdivelbiss]

That doesn't seem to have made a difference. Running the command again results in no more formatting changes.

[toku-sa-n]

See this: https://github.com/rust-osdev/uefi-rs/pull/187/checks?check_run_id=1511313923
Clippy complains about the module name. Try changing the name of loaded_image module which is inside loaded_image module. Or it may be better not to create a new loaded_image module.

[zdivelbiss]

Should be good to go now!

[GabrielMajeri]

There are a few lint warnings about missing documentation. Would it be possible to add some short doc comments for the items which lack them?

[zdivelbiss]

I don't believe the linter is complaining about anything anymore :)