Add support for disassembling CET (including endbr64), XSS, OSPKE,

Add support for disassembling CET (including endbr64), XSS, OSPKE,
clflushopt, clwb, ptwrite, rdpid, serialize, WAITPKG, and vmfunc
extensions, as well as part of TSX.  tpause and umonitor addr size
handling isn't 100% correct, but good enough to get the instruction
boundary.

Correct decoding of rex64 {fxsave,fxrstor,xsave,xrstor,xsaveopt}
to instead use a '64' suffix, ala "fxsave64".

"good enough" ok kettenis@ deraadt@ mlarkin@