target/i386: convert CMPXCHG8B/CMPXCHG16B to new decoder

target/i386: convert CMPXCHG8B/CMPXCHG16B to new decoder

The gen_cmpxchg8b and gen_cmpxchg16b functions even have the correct
prototype already; the only thing that needs to be done is removing the
gen_lea_modrm() call.

This moves the last LOCK-enabled instructions to the new decoder.  It is
now possible to assume that gen_multi0F is called only after checking
that PREFIX_LOCK was not specified.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>