fate: Do not unconditionally run libavutil tests

Now that libavutil can be disabled, this should be conditional.

tests/Makefile

@@ -98,7 +98,6 @@ FATE_SAMPLES-$(CONFIG_AVCONV) += $(FATE_SAMPLES_AVCONV)
 FATE_SAMPLES += $(FATE_SAMPLES-yes)
 
 FATE += $(FATE-yes)
-FATE += $(FATE_LIBAVUTIL)
 
 $(FATE_AVCONV) $(FATE_SAMPLES_AVCONV): avconv$(EXESUF)
 

tests/fate/libavutil.mak

@@ -53,4 +53,5 @@ FATE_LIBAVUTIL += fate-xtea
 fate-xtea: libavutil/xtea-test$(EXESUF)
 fate-xtea: CMD = run libavutil/xtea-test
 
+FATE-$(CONFIG_AVUTIL) += $(FATE_LIBAVUTIL)
 fate-libavutil: $(FATE_LIBAVUTIL)