rust: io: mem: return DevresLt from IoMem/ExclusiveIoMem::into_devres()

Implement ForLt for IoMem<'static, SIZE> and ExclusiveIoMem<'static,
SIZE> so that DevresLt can shorten the stored 'static lifetime back to
the caller's borrow lifetime via ForLt::cast_ref.

Change into_devres() to return DevresLt instead of Devres; add
DevresIoMem<SIZE> and DevresExclusiveIoMem<SIZE> type aliases.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>