Add get_level_count_mag()
Add get_level_count_mag()

This function will be re-used for lv_map's rd optimization

Change-Id: If015fe2319f6b3abdeeb3e5d3e23f705fc1454e2

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