KVM: vmx: VMXOFF emulation in vm86 should cause #UD

Unlike VMCALL, the instructions VMXOFF, VMLAUNCH and VMRESUME should cause a UD
exception in real-mode or vm86.  However, the emulator considers all these
instructions the same for the matter of mode checks, and emulation upon exit
due to #UD exception.

As a result, the hypervisor behaves incorrectly on vm86 mode. VMXOFF, VMLAUNCH
or VMRESUME cause on vm86 exit due to #UD. The hypervisor then emulates these
instruction and inject #GP to the guest instead of #UD.

This patch creates a new group for these instructions and mark only VMCALL as
an instruction which can be emulated.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>