vp9/x86: rename vp9dsp to vp9mc

It only contains the MC SIMD, other SIMD will go into different files.

libavcodec/x86/Makefile

@@ -125,4 +125,4 @@ YASM-OBJS-$(CONFIG_V210_ENCODER)       += x86/v210enc.o
 YASM-OBJS-$(CONFIG_VORBIS_DECODER)     += x86/vorbisdsp.o
 YASM-OBJS-$(CONFIG_VP3_DECODER)        += x86/hpeldsp_vp3.o
 YASM-OBJS-$(CONFIG_VP6_DECODER)        += x86/vp6dsp.o
-YASM-OBJS-$(CONFIG_VP9_DECODER)        += x86/vp9dsp.o
+YASM-OBJS-$(CONFIG_VP9_DECODER)        += x86/vp9mc.o

libavcodec/x86/vp9dsp.asm → libavcodec/x86/vp9mc.asm

@@ -1,5 +1,5 @@
 ;******************************************************************************
-;* VP9 SIMD optimizations
+;* VP9 motion compensation SIMD optimizations
 ;*
 ;* Copyright (c) 2013 Ronald S. Bultje <rsbultje gmail com>
 ;*