fate: employ better names and add a convenient shorthand for vp6 tests

tests/fate/vpx.mak

-FATE_EA_VP6 += fate-ea-vp60
-fate-ea-vp60: CMD = framecrc -i $(SAMPLES)/ea-vp6/g36.vp6
-
-FATE_EA_VP6 += fate-ea-vp61
-fate-ea-vp61: CMD = framecrc -i $(SAMPLES)/ea-vp6/MovieSkirmishGondor.vp6 -t 4
-
-FATE_AVCONV += $(FATE_EA_VP6)
-fate-ea-vp6: $(FATE_EA_VP6)
-
 FATE_VP3 += fate-vp31
 fate-vp31: CMD = framecrc -i $(SAMPLES)/vp3/vp31.avi
 
@@ -19,12 +10,21 @@ fate-vp3: $(FATE_VP3)
 FATE_AVCONV += fate-vp5
 fate-vp5: CMD = framecrc -i $(SAMPLES)/vp5/potter512-400-partial.avi -an
 
-FATE_AVCONV += fate-vp6a
+FATE_VP6 += fate-vp60
+fate-vp60: CMD = framecrc -i $(SAMPLES)/ea-vp6/g36.vp6
+
+FATE_VP6 += fate-vp61
+fate-vp61: CMD = framecrc -i $(SAMPLES)/ea-vp6/MovieSkirmishGondor.vp6 -t 4
+
+FATE_VP6 += fate-vp6a
 fate-vp6a: CMD = framecrc -i $(SAMPLES)/flash-vp6/300x180-Scr-f8-056alpha.flv
 
-FATE_AVCONV += fate-vp6f
+FATE_VP6 += fate-vp6f
 fate-vp6f: CMD = framecrc -i $(SAMPLES)/flash-vp6/clip1024.flv
 
+FATE_AVCONV += $(FATE_VP6)
+fate-vp6: $(FATE_VP6)
+
 VP8_SUITE = 001 002 003 004 005 006 007 008 009 010 011 012 013 014 015 016 017
 
 define FATE_VP8_SUITE