Make mi_width/height_log2_lookup table support 4x4 mode_info unit

Change the table content to support 4x4 mode_info unit. Refactor
partition_plane_context() to reflect the fact that the minimum
partition block size is 8x8.

Change-Id: Id26fcfba8d74efdb9ae316c9d066cd65358dd7e6
2 files changed