Support ETC1 compression in atlastool.
Support ETC1 compression in atlastool.

libretro/ppsspp-native,zhykzhykzhyk/ppsspp-native,zhykzhykzhyk/ppsspp-native,unknownbrackets/native,libretro/ppsspp-native,hrydgard/native,unknownbrackets/native,unknownbrackets/native,zhykzhykzhyk/ppsspp-native,libretro/ppsspp-native,hrydgard/native,unknownbrackets/native,hrydgard/native,libretro/ppsspp-native,hrydgard/native,zhykzhykzhyk/ppsspp-native