Xfermode: SSE2 implementation of multiply_modeproc

Xfermode: SSE2 implementation of multiply_modeproc

This patch implements basics for Xfermode SSE optimization. Based on
these basics, SSE2 implementation of multiply_modeproc is provided. SSE2
implementation for other modes will come in future. With this patch
performance of Xfermode_Multiply will improve about 45%. Here are the
data on desktop i7-3770.
before:
Xfermode_Multiply   8888:  cmsecs =     33.30   565:  cmsecs =     45.65
after:
Xfermode_Multiply   8888:  cmsecs =     17.18   565:  cmsecs =     24.87

BUG=
R=mtklein@google.com

Author: qiankun.miao@intel.com

Review URL: https://codereview.chromium.org/202903004

git-svn-id: http://skia.googlecode.com/svn/trunk@14006 2bbb7eff-a529-9590-31e7-b0007b416f81