i386/cpu: Rename enable_cpuid_0x1f to force_cpuid_0x1f

i386/cpu: Rename enable_cpuid_0x1f to force_cpuid_0x1f

The name of "enable_cpuid_0x1f" isn't right to its behavior because the
leaf 0x1f can be enabled even when "enable_cpuid_0x1f" is false.

Rename it to "force_cpuid_0x1f" to better reflect its behavior.

Suggested-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Link: https://lore.kernel.org/r/20250603050305.1704586-2-xiaoyao.li@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>