i386/kvm: add support for Hyper-V TLB flush

i386/kvm: add support for Hyper-V TLB flush

Add support for Hyper-V TLB flush which recently got added to KVM.

Just like regular Hyper-V we announce HV_EX_PROCESSOR_MASKS_RECOMMENDED
regardless of how many vCPUs we have. Windows is 'smart' and uses less
expensive non-EX Hypercall whenever possible (when it wants to flush TLB
for all vCPUs or the maximum vCPU index in the vCPU set requires flushing
is less than 64).

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20180610184927.19309-1-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>