ARM: set section to .text in 'function' macro

This ensures code always goes into the .text section and avoids the
need to specify it explicitly after changing sections.

Originally committed as revision 24095 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/arm/asm.S

@@ -40,6 +40,7 @@ ELF     .size   \name, . - \name
         .endfunc
         .purgem endfunc
     .endm
+        .text
     .if \export
         .global EXTERN_ASM\name
 EXTERN_ASM\name: