Super FX: Remove massive amounts of indirection starting in FxEmulate.

* FxEmulate now uses fx_run directly.
* Pointers to function pointers that were formerly selected according to whether Super FX breakpoints are enabled are replaced with references to the actual array. This allows the linker to insert constant addresses.
* Super FX breakpoints are now unsupported.
Super FX: Use a local variable to hold the number of instructions left to execute.

The uses of global variables 'GSU.vCounter' and 'GSU.vInstCount' are deleted with this commit. Local variables can be kept in registers and, in that case, there are no stores to memory before each opcode function is executed.
fxinst.h: Delete unused members of 'struct FxRegs_s'.