x86: misc further register-only insns don't need to go through mod_table[]

x86: misc further register-only insns don't need to go through mod_table[]

Several already use OP_R(), which rejects the memory forms of insns, and
a few others can easily be converted to do so as well. Note that for it
to be able to use BadOp() without forward declaration, OP_Skip_MODRM() is
moved down.

While there add the previously missing PREFIX_OPCODE to legacy opcode
0FD7.