add REGd definition

Originally committed as revision 12481 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/x86_cpu.h

@@ -38,6 +38,7 @@
 #    define REGa    rax
 #    define REGb    rbx
 #    define REGc    rcx
+#    define REGd    rdx
 #    define REGSP   rsp
 
 #else
@@ -56,6 +57,7 @@
 #    define REGa    eax
 #    define REGb    ebx
 #    define REGc    ecx
+#    define REGd    edx
 #    define REGSP   esp
 #endif