libweston: extract dep_gbm from backend-drm

Move the dep_gbm from the backend-drm specific meson.build to the common
libweston meson.build to be able to use it in other modules, too.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>

libweston/backend-drm/meson.build

@@ -58,7 +58,6 @@ deps_drm = [
 ]
 
 if get_option('renderer-gl')
-	dep_gbm = dependency('gbm', required: false, version: '>= 21.1.1')
 	if not dep_gbm.found()
 		error('drm-backend with GL renderer requires gbm which was not found. Or, you can use \'-Drenderer-gl=false\'.')
 	endif

libweston/meson.build

@@ -87,6 +87,8 @@ srcs_libweston = [
 subdir('desktop')
 subdir('shell-utils')
 
+dep_gbm = dependency('gbm', required: false, version: '>= 21.1.1')
+
 if get_option('backend-vnc')
 	dep_pam = dependency('pam', required: false)
 	if not dep_pam.found()