KVM: Emulate multibyte NOP

This is encountered when booting RHEL5.9 64-bit.  There is another bug
after this one that is not a simple emulation failure, but this one lets
the boot proceed a bit.

Cc: <stable@vger.kernel.org> # 3.9
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>