i386: Disable TOPOEXT by default on "-cpu host"

Enabling TOPOEXT is always allowed, but it can't be enabled
blindly by "-cpu host" because it may make guests crash if the
rest of the cache topology information isn't provided or isn't
consistent.

This addresses the bug reported at:
https://bugzilla.redhat.com/show_bug.cgi?id=1613277Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Message-Id: <20180809221852.15285-1-ehabkost@redhat.com>
Tested-by: NRichard W.M. Jones <rjones@redhat.com>
Reviewed-by: NBabu Moger <babu.moger@amd.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

target/i386/cpu.c

@@ -849,6 +849,12 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
         },
         .cpuid_eax = 0x80000001, .cpuid_reg = R_ECX,
         .tcg_features = TCG_EXT3_FEATURES,
+        /*
+         * TOPOEXT is always allowed but can't be enabled blindly by
+         * "-cpu host", as it requires consistent cache topology info
+         * to be provided so it doesn't confuse guests.
+         */
+        .no_autoenable_flags = CPUID_EXT3_TOPOEXT,
     },
     [FEAT_C000_0001_EDX] = {
         .feat_names = {