fate/filter: move gradfun filtergraph to a dedicated script.

tests/fate/filter.mak

@@ -113,7 +113,7 @@ FATE_FILTER-$(call ALLYES, UTVIDEO_DECODER AVI_DEMUXER PERMS_FILTER CURVES_FILTE
 fate-filter-curves: CMD = framecrc -i $(SAMPLES)/utvideo/utvideo_rgb_median.avi -vf perms=random,curves=vintage
 
 FATE_FILTER-$(call ALLYES, VMD_DEMUXER VMDVIDEO_DECODER FORMAT_FILTER PERMS_FILTER GRADFUN_FILTER) += fate-filter-gradfun-sample
-fate-filter-gradfun-sample: CMD = framecrc -i $(SAMPLES)/vmd/12.vmd -vf "sws_flags=+accurate_rnd+bitexact;format=gray,perms=random,gradfun=10:8" -an -frames:v 20
+fate-filter-gradfun-sample: CMD = framecrc -i $(SAMPLES)/vmd/12.vmd -filter_script $(SRC_PATH)/tests/filtergraphs/gradfun -an -frames:v 20
 
 FATE_FILTER-$(call ALLYES, TESTSRC_FILTER SINE_FILTER CONCAT_FILTER) += fate-filter-concat
 fate-filter-concat: CMD = framecrc -filter_complex_script $(SRC_PATH)/tests/filtergraphs/concat

tests/filtergraphs/gradfun

+sws_flags=+accurate_rnd+bitexact;
+format=gray, perms=random, gradfun=10:8