Fix compile error on bfin.

After the removal of all Blackfin architecture optimizations in
http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=b55d3bbeed375f7b74442c4dd274d116a3e3d2e1
some includes were left behind leading to a compilation error

http://autobuild.buildroot.net/results/ae0/ae056f267e907091d09d2a1546d6f1ae02fa23b9/

CC      libavformat/adtsenc.o
In file included from ./libavcodec/get_bits.h:35,
                 from ./libavcodec/ac3_parser.h:27,
                 from libavformat/ac3dec.c:23:
./libavcodec/mathops.h:43:29: error: bfin/mathops.h: No such file or directory

Patch sent upstream:
https://ffmpeg.org/pipermail/ffmpeg-devel/2014-August/160694.html

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>

diff -uNr ffmpeg-2.3.1.org/libavcodec/mathops.h ffmpeg-2.3.1/libavcodec/mathops.h
--- ffmpeg-2.3.1.org/libavcodec/mathops.h	2014-07-31 03:18:40.000000000 +0200
+++ ffmpeg-2.3.1/libavcodec/mathops.h	2014-08-04 20:49:00.340763801 +0200
@@ -39,8 +39,6 @@
 #   include "arm/mathops.h"
 #elif ARCH_AVR32
 #   include "avr32/mathops.h"
-#elif ARCH_BFIN
-#   include "bfin/mathops.h"
 #elif ARCH_MIPS
 #   include "mips/mathops.h"
 #elif ARCH_PPC
diff -uNr ffmpeg-2.3.1.org/libavutil/bswap.h ffmpeg-2.3.1/libavutil/bswap.h
--- ffmpeg-2.3.1.org/libavutil/bswap.h	2014-07-31 03:18:47.000000000 +0200
+++ ffmpeg-2.3.1/libavutil/bswap.h	2014-08-04 20:48:56.028818009 +0200
@@ -40,8 +40,6 @@
 #   include "arm/bswap.h"
 #elif ARCH_AVR32
 #   include "avr32/bswap.h"
-#elif ARCH_BFIN
-#   include "bfin/bswap.h"
 #elif ARCH_SH4
 #   include "sh4/bswap.h"
 #elif ARCH_X86
diff -uNr ffmpeg-2.3.1.org/libavutil/timer.h ffmpeg-2.3.1/libavutil/timer.h
--- ffmpeg-2.3.1.org/libavutil/timer.h	2014-07-31 03:18:47.000000000 +0200
+++ ffmpeg-2.3.1/libavutil/timer.h	2014-08-04 20:48:48.832908474 +0200
@@ -40,8 +40,6 @@
 
 #if   ARCH_ARM
 #   include "arm/timer.h"
-#elif ARCH_BFIN
-#   include "bfin/timer.h"
 #elif ARCH_PPC
 #   include "ppc/timer.h"
 #elif ARCH_X86