gl-drm: Fix missing link to gbm for ecore_evas_drm and clean up build script

gl-drm: Fix missing link to gbm for ecore_evas_drm and clean up build script

@fix

Summary:
This fixes following build script problems for ecore_evas_drm engine module.

1. Missing link to gbm for ecore_evas_drm if '--enable-gl-drm' option is given.
ecore_evas_drm engine is using gbm function if it builds with that config option.
To be more exact, ecore_evas_gl_drm_new_internal function needs gbm.
Thus we need to add gbm library linking '-lgbm' to ecore_evas_drm engine module
if '--enable-gl-drm' option is given. I've added this build script to
m4/ecore_check_module.m4 file.

2. Wrong gbm dependency check code in configure.ac
EFL_OPTIONAL_INTERNAL_DEPEND_PKG m4 macro function is designed for checking
dependency of efl internal libraries. Thus we should remove gbm pkg name when
configuring ecore_evas_drm engine module. It would be better to move dependency
check for gbm to m4/ecore_check_module.m4 file. And one more thing want_drm
value has to be changed to want_gl_drm in ECORE_EVAS_MODULE([gl-drm]...).

3. BUILD_ECORE_EVAS_OPENGL_DRM macro is always defined in configure.ac.
This kind of macro, BUILD_EFL_MODULE_NAME, has to be defined only if given module
is enabled. But this macro value was just defined with no test.
And it is even useless, we can use BUILD_ECORE_EVAS_GL_DRM macro which is defined
by ECORE_EVAS_MODULE([gl-drm], [${want_gl_drm}],...) function.
So I've removed that from configure.ac.

Test Plan:
1. Configure with --enable-gl-drm:
  $ ./autogen.sh --enable-drm --enable-gl-drm
2. Build:
  $ make && make install
3. Check module.so of ecore_evas_drm engine whether it has a library dependency with gbm:
  $ readelf -a $EFL_GIT/src/modules/ecore_evas/engines/drm/.libs/module.so | grep NEEDED

Reviewers: raster, stefan_schmidt, devilhorns

Reviewed By: devilhorns

Subscribers: cedric

Differential Revision: https://phab.enlightenment.org/D1379