i386/cpu: Introduce enable_cpuid_0x1f to force exposing CPUID 0x1f

i386/cpu: Introduce enable_cpuid_0x1f to force exposing CPUID 0x1f

Currently, QEMU exposes CPUID 0x1f to guest only when necessary, i.e.,
when topology level that cannot be enumerated by leaf 0xB, e.g., die or
module level, are configured for the guest, e.g., -smp xx,dies=2.

However, TDX architecture forces to require CPUID 0x1f to configure CPU
topology.

Introduce a bool flag, enable_cpuid_0x1f, in CPU for the case that
requires CPUID leaf 0x1f to be exposed to guest.

Introduce a new function x86_has_cpuid_0x1f(), which is the wrapper of
cpu->enable_cpuid_0x1f and x86_has_extended_topo() to check if it needs
to enable cpuid leaf 0x1f for the guest.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250508150002.689633-34-xiaoyao.li@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>