KVM: nVMX: Success/failure of VMX instructions.

VMX instructions specify success or failure by setting certain RFLAGS bits.
This patch contains common functions to do this, and they will be used in
the following patches which emulate the various VMX instructions.

Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>