Refactor av1_get_palette_color_index_context()
Refactor av1_get_palette_color_index_context()

Change-Id: Ib9464af6e60c485fa77ecada0fc4ce5402d42988

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom