i386/cpu: Add default cache model for Intel CPUs with level < 4

i386/cpu: Add default cache model for Intel CPUs with level < 4

Old Intel CPUs with CPUID level < 4, use CPUID 0x2 leaf (if available)
to encode cache information.

Introduce a cache model "legacy_intel_cpuid2_cache_info" for the CPUs
with CPUID level < 4, based on legacy_l1d_cache, legacy_l1i_cache,
legacy_l2_cache_cpuid2 and legacy_l3_cache. But for L2 cache, this
cache model completes self_init, sets, partitions, no_invd_sharing and
share_level fields, referring legacy_l2_cache, to avoid someone
increases CPUID level manually and meets assert() error. But the cache
information present in CPUID 0x2 leaf doesn't change.

This new cache model makes it possible to remove legacy_l2_cache_cpuid2
in X86CPUState and help to clarify historical cache inconsistency issue.

Furthermore, apply this legacy cache model to all Intel CPUs with CPUID
level < 4. This includes not only "pentium2" and "pentium3" (which have
0x2 leaf), but also "486" and "pentium" (which only have 0x1 leaf, and
cache model won't be presented, just for simplicity).

A legacy_intel_cpuid2_cache_info cache model doesn't change the cache
information of the above CPUs, because they just depend on 0x2 leaf.

Only when someone adjusts the min-level to >=4 will the cache
information in CPUID leaf 4 differ from before: previously, the L2
cache information in CPUID leaf 0x2 and 0x4 was different, but now with
legacy_intel_cpuid2_cache_info, the information they present will be
consistent. This case almost never happens, emulating a CPUID that is
not supported by the "ancient" hardware is itself meaningless behavior.

Therefore, even though there's the above difference (for really rare
case) and considering these old CPUs ("486", "pentium", "pentium2" and
"pentium3") won't be used for migration, there's no need to add new
versioned CPU models

Tested-by: Yi Lai <yi1.lai@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250711102143.1622339-4-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>