cpu: fix IDT and GDT lifetimes on load methods

[00xc]

When running the LIDT or LGDT instructions, we pass addresses pointing to architecture-specific tables that the CPU will use during operation. These tables must reside on valid memory during CPU operation to avoid malfunction.

In practical terms, this means the GDT and IDT entries must have a static lifetime. This will avoid at compile time the following construct:

{
    let idt = IDT::new();
    idt.load();
}
// the IDT entries are no longer valid here

We could enforce this at the type level by requiring the load() method on these structs to take a &'static lifetime. However, since we use locking, we cannot get such reference, only a reference that lives as long as a lock guard we get from the lock protecting the struct. However, this does not matter, as we can check that the guard points to a struct with static lifetime (Guard<'static, T>).

Thus, rewrite the methods on these structs that have these requirements such that they take a guard pointing to a 'static IDT or GDT.

[p4zuu]

This is partially fixing #359.