Destroy all FBOs/textures upon sceKernelLoadExec().

It can confuse our heuristics about size, attachment, memcpy, etc.
Revert the early wake of threads for io waits.

This reverts commit 610ada87214c60a8e5b1f5f742135abbc5cf2544.

It makes sense to let these run longer.  Apparently this caused problems
in Castlevania, see #6432.
Merge pull request #6450 from unknownbrackets/gpu-blocktransfer

Clear framebuffers/textures upon sceKernelLoadExec()