[X86] Force VIA PadLock crypto instructions to emit a 0xF3 prefix when they...

[X86] Force VIA PadLock crypto instructions to emit a 0xF3 prefix when they encode to match what GNU as does.

The spec for these says they need 0xf3 but also mentions REP
before the mnemonic. But I don't think its fair to users to make
them write REP first. And gas doesn't make them. objdump seems to
disassemble with or without the prefix and just prints any 0xf3
as REP.