Add palette mode for keyframe luma channel. Palette mode is enabled
when using "--tune-content=screen" in encoding config parameters.
on screen_content testset: +6.89%
on derlr : +0.00%
Design doc (WIP):
https://goo.gl/lD4yJw
Change-Id: Ib368b216bfd3ea21c6c27436934ad87afdaa6f88
This commit removes mbmi_ext_base pointer from MACROBLOCK struct.
Its use case can be fully covered by cpi->mbmi_ext_base pointer.
Change-Id: I155351609336cf5b6145ed13c21b105052727f30