KVM: x86: Emulator mis-decodes VEX instructions on real-mode

KVM: x86: Emulator mis-decodes VEX instructions on real-mode

Commit 371dda17fa82 (KVM: x86: Mark VEX-prefix instructions emulation as
unimplemented, 2014-06-02) marked VEX instructions as such in protected
mode.  VEX-prefix instructions are not supported relevant on real-mode
and VM86, but should cause #UD instead of being decoded as LES/LDS.

Fix this behaviour to be consistent with real hardware.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
[Check for mod == 3, rather than 2 or 3. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>