Make bindgen optional

[lilianmoraru]

The code was ported to use bindgen but it considerably affects compilation times.
bindgen should be optional:

• Without bindgen: compiling dlt-daemon 2.17 bindings(Currently needs an update from 2.16)
• With bindgen: compiling whatever the dlt-daemon reference is set to

[lilianmoraru]

Closing this issue:

• The public API was not changed in these headers(these are all the headers for which bindings were written by hand): dlt_common, dlt_shm, dlt_types and dlt_user.
• The submodule was updated.

[lilianmoraru]

Ups, reopening since the second point of making bindgen actually optional, was not implemented.