Extend left/above partition context to per mi(8x8)

Update and buffer left/above partition information context per 8x8
block. This allows to further enable recursive partition down to
4x4 block size, and hence deprecating I4X4_PRED and SPLITMV.

This commit also fixes a context buffer swap/restore issue in 32x32
partition type search. This gives 0.1% performance gain for derf/yt.
Will refactor the superblock partition type search into recursion
form.

Change-Id: Ib61975aca5f12b78d8018481d7fa1393d085689b