KVM: VMX: Read & store IDT_VECTORING_INFO_FIELD

We'll want to write to it in order to fix real-mode irq injection problems,
but it is a read-only field.  Storing it in a variable solves that issue.

Signed-off-by: Avi Kivity <avi@qumranet.com>

diff --cc drivers/kvm/vmx.c
Simple merge