Texture updates have been moved into TextureCache, while
TMEM updates where moved into bpmem. Code for handling
efb2ram updates was added to TextureCache.
There was a bug for preloaded RGBA8 textures, it only copied
half the texture. The TODO was wrong too.
This is required to make packing consistent between compilers: with u32, MSVC
would not allocate a bitfield that spans two u32s (it would leave a "hole").