modules: lz4: add configurability

- Add possibility to disable functions that use heap. This is to
  reduce code size and prevent accidental use of heap.

- Add possibility to compile xxhash library, "Extremely Fast Hash
  algorithm" in. It might be sometimes needed as a standalone,
  but especially lz4frame requires it.

- Add possibility to compile also hc and lz4frame modules. The
  config options include possibility to configure will heap or
  stack be used. Defaults are set according to lz4's current
  defaults.

Signed-off-by: Miika Karanki <miika.karanki@vaisala.com>