The normal textures were generated from the corresponding diffuse textures with the Basic (free) version of ShaderMap 4 tool because it produces way better results than the popular free online generators I tried. ShaderMap Basic allows non-commercial use, and I believe Enderal SE fits into this category. Also their site says something about "no watermarks" for the pro version, but I failed to notice any watermarks in the result textures, so it's not like there will be "SHADERMAP" written over all wooden textures in Ark or something.