vp9: Choose the scheme for modeling rd for 32x32 based on skin color.
vp9: Choose the scheme for modeling rd for 32x32 based on skin color.

For real time CBR mode, use model_rd_for_sb_y for 32x32 if the sb is
a skin sb to avoid visual regression on the slowly moving face.

Refer to the cl: https://chromium-review.googlesource.com/#/c/356020/

Change-Id: I42c36666b2b474ce5ee274239d52ae8ab400fd46

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