fix: derive Default for kvm_xsave2

`FamStructWrapper<T>` imposes a bound of `Default + FamStruct` on `T`.
However, it seems that when defining type aliases, Rust will not ensure
this bound is met until the type alias is actually used (as in a
function definition). This made the `Xsave` type defined in
`x86_64/fam.rs` essentially "unmentionable", as any attempts as using it
will result in a compile error.

Fix this by deriving `Default` for it, and also derive `Debug` for
consistency with other types.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

Author: roypat

src/x86_64/fam_wrappers.rs

@@ -98,6 +98,7 @@ pub type MsrList = FamStructWrapper<kvm_msr_list>;
 ///
 /// See also: [`Xsave`].
 #[repr(C)]
+#[derive(Debug, Default)]
 pub struct kvm_xsave2 {
     pub len: usize,
     pub xsave: kvm_xsave,