i386: hvf: inject General Protection Fault when vmexit through vmcall

This patch injects a GP fault when the guest vmexit's by executing a
vmcall instruction.

Signed-off-by: Sergio Andres Gomez Del Real <Sergio.G.DelReal@gmail.com>
Message-Id: <20170913090522.4022-15-Sergio.G.DelReal@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
