rmode_segment_valid() checks if segment descriptor can be used to enter
vm86 mode. VMX spec mandates that in vm86 mode CS register will be of
type data, not code. Lets allow guest entry with vm86 mode if the only
problem with CS register is incorrect type. Otherwise entire real mode
will be emulated.

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>