In case interrupts are delayed, read cmd early.

Otherwise, in Project Diva, the cmd may be overwritten (probably due to a
sync or etc.) by some other cmd.  Fixes #5896.
Split out a few more common cmds.
Fix ridiculously bad typo.
Split out viewport type commands.
Split out the bounding box and stencil test cmds.
Split out the clutformat cmd as well.
Merge pull request #5903 from unknownbrackets/gpu-minor

More splitting, fix late GE interrupts reading wrong data