make high precision mode accessible at compile time

Originally committed as revision 8470 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/resample2.c

@@ -30,7 +30,7 @@
 #include "common.h"
 #include "dsputil.h"
 
-#if 1
+#ifndef CONFIG_RESAMPLE_HP
 #define FILTER_SHIFT 15
 
 #define FELEM int16_t