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.
Allow rescheduling within callbacks.
Remove outdated comment (real cause found/fixed.)
Simplify __KernelReSchedule().

It no longer needs all these checks, and we can Advance within callbacks,
interrupts, etc. safely.
Avoid Advance() twice, cleanup some comments.
Merge pull request #6452 from unknownbrackets/callbacks

Allow rescheduling within a callback
Merge pull request #6450 from unknownbrackets/gpu-blocktransfer

Clear framebuffers/textures upon sceKernelLoadExec()
Allow changing software skinning at runtime.
Allow changing prescale uv at runtime.
Move GLLost to NativeInit/NativeShutdown.

Otherwise, we clear the registered holders when the display turns off, and
never remember them.  This causes the vertex cache to stop working, for
example.
Merge pull request #6459 from unknownbrackets/gllost-fix

Move GL lost manager to NativeInit/NativeShutdown
Merge pull request #6456 from unknownbrackets/gpu-minor

Allow changing software skinning and prescale uv at runtime