Lisp is "functional-enabling" not a functional language. Take a look at the Common Lisp library and you'll see a whole lot of imperative-nature constructs and code in it. Lisp permits (and to a degree supports) functional programming. It does not enforce nor even default to the functional paradigm.

And even in a Lisp you're going to start hitting the boundaries of your kit in the embedded world when you do partial application, closures, and even something as seemingly trivial as using immutable state. You'll wind up fighting the language more often than fighting your problem domain and the result will be counterproductive.

Best of breed for me in embedded space is Ada (with Modula-3 being another decent choice). Lisp's not even in the display hall.