move vp9_avg to vpx_dsp

test/avg_test.cc

test/test.mk

vp10/common/vp10_rtcd_defs.pl

vp10/encoder/encodeframe.c

vp10/encoder/mcomp.c

vp10/vp10cx.mk

vp9/common/vp9_rtcd_defs.pl

vp9/encoder/arm/neon/vp9_avg_neon.c

vp9/encoder/mips/msa/vp9_avg_msa.c

vp9/encoder/vp9_avg.c

vp9/encoder/vp9_encodeframe.c

vp9/encoder/vp9_mcomp.c

vp9/encoder/vp9_pickmode.c

vp9/encoder/x86/vp9_avg_intrin_sse2.c

vp9/encoder/x86/vp9_dct_ssse3_x86_64.asm

vp9/vp9cx.mk

vpx_dsp/arm/avg_neon.c

vpx_dsp/avg.c

vpx_dsp/mips/avg_msa.c

vpx_dsp/vpx_dsp.mk