KVM: enlarge number of possible CPUID leaves

Currently the number of CPUID leaves KVM handles is limited to 40.
My desktop machine (AthlonII) already has 35 and future CPUs will
expand this well beyond the limit. Extend the limit to 80 to make
room for future processors.

KVM-Stable-Tag.
Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>