i386/kvm: add a comment explaining why .feat_names are commented out for Hyper-V feature bits

Hyper-V .feat_names are, unlike hardware features, commented out and it is
not obvious why we do that. Document the current status quo.
Signed-off-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20181221141604.16935-1-vkuznets@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

target/i386/cpu.c

@@ -929,6 +929,13 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
          */
         .no_autoenable_flags = ~0U,
     },
+    /*
+     * .feat_names are commented out for Hyper-V enlightenments because we
+     * don't want to have two different ways for enabling them on QEMU command
+     * line. Some features (e.g. "hyperv_time", "hyperv_vapic", ...) require
+     * enabling several feature bits simultaneously, exposing these bits
+     * individually may just confuse guests.
+     */
     [FEAT_HYPERV_EAX] = {
         .type = CPUID_FEATURE_WORD,
         .feat_names = {