i386/cpu: Add descriptor 0x49 for CPUID 0x2 encoding

i386/cpu: Add descriptor 0x49 for CPUID 0x2 encoding

The legacy_l2_cache (2nd-level cache: 4 MByte, 16-way set associative,
64 byte line size) corresponds to descriptor 0x49, but at present
cpuid2_cache_descriptors doesn't support descriptor 0x49 because it has
multiple meanings.

The 0x49 is necessary when CPUID 0x2 and 0x4 leaves have the consistent
cache model, and use legacy_l2_cache as the default L2 cache.

Therefore, add descriptor 0x49 to represent general L2 cache.

Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: Yi Lai <yi1.lai@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250711102143.1622339-3-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>