KVM: x86: expose cpuid_entry2_find for TDX

KVM: x86: expose cpuid_entry2_find for TDX

CPUID values are provided for TDX virtual machines as part of the
KVM_TDX_INIT_VM ioctl.  Unlike KVM_SET_CPUID2, TDX will need to
examine the leaves, either to validate against the CPUIDs listed
in the TDX modules configuration or to fill other controls with
matching values.

Since there is an existing function to look up a leaf/index pair
into a given list of CPUID entries, export it as kvm_find_cpuid_entry2().

Reviewed-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>