Support FNOP in m68k disassembly

[huth]

The 68881/68882 user manual and the 68040 user manually explicitely lists FNOP as a separate FPU instruction. However, Capstone currently disassembles this as FBF instead:

 $ cstool m68k40 0xf2800000
 0  f2 80 00 00  fbf.w	$2

According to the 68881/68882 user manual, FNOP has some special sync'ing capabilities, so it seems to be different from the other FBcc instructions and thus I think Capstone should properly disassemble this as FNOP instead of FBF.