deprecate av_parse_cpu_flags

This function is problematic in several ways, its also quite
unpredictable which flags it ends up turning on
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/cpu.h

@@ -87,6 +87,7 @@ attribute_deprecated void av_set_cpu_flags_mask(int mask);
  * Please use av_parse_cpu_caps() when possible.
  * @return a combination of AV_CPU_* flags, negative on error.
  */
+attribute_deprecated
 int av_parse_cpu_flags(const char *s);
 
 /**