build: codegen generation should depend on elementary_codegen

build: codegen generation should depend on elementary_codegen

Summary:
otherwise buildfailures like :

/usr/bin/env EFL_RUN_IN_TREE=1 /Users/travis/build/Enlightenment/efl/build/src/bin/elementary/elementary_codegen -p=codegen_example src/examples/elementary/codegen_example.edj elm/example/mylayout/default src/examples/elementary/codegen_example_generated.c src/examples/elementary/codegen_example_generated.h

Can appear.

Reviewers: zmike

Reviewed By: zmike

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D8428