Don't reset OFFSETADDR, changes offsetAddr.
Allow individual cmd funcs to be called.

Rather than a single one, ExecuteOpInternal().  This allows less "huge
switch" code organization, and will (once separated) also improve speed.
Move a few GE cmds to separate funcs.

2% improvement in God Eater 2.
Add the common funcs to the direct exec calls.
Split out more of the top GE cmd funcs.
Keep flags and func together.

Seems not to make a big difference, though.
Merge pull request #5898 from unknownbrackets/gpu-cmd-funcs

Use individual funcs, skipping the ExecuteOpInternal switch