avcodec/mips: [loongson] optimize put_hevc_qpel_hv_8 with mmi.

Optimize put_hevc_qpel_hv_8 with mmi in the case width=4/8/12/16/24/32/48/64.
This optimization improved HEVC decoding performance 11%(1.81x to 2.01x, tested on loongson 3A3000).

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/mips/mmiutils.h

@@ -250,6 +250,15 @@
       : "memory"                                                \
     );
 
+/**
+ * brief: Transpose 2X2 word packaged data.
+ * fr_i0, fr_i1: src
+ * fr_o0, fr_o1: dst
+ */
+#define TRANSPOSE_2W(fr_i0, fr_i1, fr_o0, fr_o1)                          \
+        "punpcklwd  "#fr_o0",   "#fr_i0",   "#fr_i1"                \n\t" \
+        "punpckhwd  "#fr_o1",   "#fr_i0",   "#fr_i1"                \n\t"
+
 /**
  * brief: Transpose 4X4 half word packaged data.
  * fr_i0, fr_i1, fr_i2, fr_i3: src & dst