nested vmx: emulate MSR bitmaps

nested vmx: emulate MSR bitmaps

In nested vmx virtualization for MSR bitmaps, L0 hypervisor will trap
all the VM exit from L2 guest by disable the MSR_BITMAP feature. When
handling this VM exit, L0 hypervisor judges whether L1 hypervisor uses
MSR_BITMAP feature and the corresponding bit is set to 1. If so, L0
will inject such VM exit into L1 hypervisor; otherwise, L0 will be
responsible for handling this VM exit.

Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Committed-by: Keir Fraser <keir@xen.org>