Changes/cleanup to TextureCache::Load and other mipmap related code.
The significant change is what is now line 520 of TextureCacheBase.cpp:
((std::max(mipWidth, bsw) * std::max(mipHeight, bsh) * bsdepth) >> 1)
to
TexDecoder_GetTextureSizeInBytes(expanded_mip_width, expanded_mip_height, texformat);

Fixes issue 5328.
Fixes issue 5461.