ARM: add missing preserve8 directives

Originally committed as revision 21952 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/arm/dsputil_armv6.S

@@ -20,6 +20,8 @@
 
 #include "asm.S"
 
+        preserve8
+
         .text
 
 .macro  call_2x_pixels  type, subp

libavcodec/arm/mdct_neon.S

@@ -21,6 +21,8 @@
 
 #include "asm.S"
 
+        preserve8
+
         .text
 
 #define ff_fft_calc_neon X(ff_fft_calc_neon)