KVM: x86: hyperv: optimize sparse VP set processing

KVM: x86: hyperv: optimize sparse VP set processing

Rewrite kvm_hv_flush_tlb()/send_ipi_vcpus_mask() making them cleaner and
somewhat more optimal.

hv_vcpu_in_sparse_set() is converted to sparse_set_to_vcpu_mask()
which copies sparse banks u64-at-a-time and then, depending on the
num_mismatched_vp_indexes value, returns immediately or does
vp index to vcpu index conversion by walking all vCPUs.

To support the change and make kvm_hv_send_ipi() look similar to
kvm_hv_flush_tlb() send_ipi_vcpus_mask() is introduced.

Suggested-by: Roman Kagan <[email protected]>
Signed-off-by: Vitaly Kuznetsov <[email protected]>
Reviewed-by: Roman Kagan <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>