rust: error: add `From` implementations for `Error`

Add a set of `From` implementations for the `Error` kernel type.

These implementations allow to easily convert from standard Rust
error types to the usual kernel errors based on one of the `E*`
integer codes.

On top of that, the question mark Rust operator (`?`) implicitly
performs a conversion on the error value using the `From` trait
when propagating. Thus it is extra convenient to use.

For instance, a kernel function that needs to convert a `i64` into
a `i32` and to bubble up the error as a kernel error may write:

    fn f(x: i64) -> Result<...> {
        ...
        let y = i32::try_from(x)?;
        ...
    }

which will transform the `TryFromIntError` into an `Err(EINVAL)`.

Co-developed-by: Adam Bratschi-Kaye <[email protected]>
Signed-off-by: Adam Bratschi-Kaye <[email protected]>
Co-developed-by: Nándor István Krácser <[email protected]>
Signed-off-by: Nándor István Krácser <[email protected]>
Signed-off-by: Wedson Almeida Filho <[email protected]>
Reviewed-by: Finn Behrens <[email protected]>
[Reworded, adapted for upstream and applied latest changes]
Signed-off-by: Miguel Ojeda <[email protected]>

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