asm: luma_vpp[48x64] in avx2: improve 21298c->14696c
asm: luma_vpp[24x32] in avx2: improve 5637c->3695c
asm: luma_vpp[12x16] in avx2: improve 1977c->1418c
asm: luma_vpp[8x16, 8x32] in avx2: improve 1139c->774c, 1968c->1452c
encoder: free csv file name

Since strdup is used uniformly for filenames, csvfn cannot be const.
x265: add ratetol to command line help