target/i386: suppress CPUID leaves not defined by the CPU vendor

Currently all built-in CPUs report cache information via CPUID leaves 2
and 4, but these have never been defined for AMD. In the case of
SEV-SNP this can cause issues with CPUID enforcement. Address this by
allowing CPU types to suppress these via a new "x-vendor-cpuid-only"
CPU property, which is true by default, but switched off for older
machine types to maintain compatibility.

Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: zhenwei pi <pizhenwei@bytedance.com>
Suggested-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Message-Id: <20210708003623.18665-1-michael.roth@amd.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>