Documentation: kvm: document CPUID bit for MSR_KVM_POLL_CONTROL

Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Documentation/virtual/kvm/cpuid.txt

@@ -66,6 +66,10 @@ KVM_FEATURE_PV_SEND_IPI            ||    11 || guest checks this feature bit
                                    ||       || before using paravirtualized
                                    ||       || send IPIs.
 ------------------------------------------------------------------------------
+KVM_FEATURE_PV_POLL_CONTROL        ||    12 || host-side polling on HLT can
+                                   ||       || be disabled by writing
+                                   ||       || to msr 0x4b564d05.
+------------------------------------------------------------------------------
 KVM_FEATURE_PV_SCHED_YIELD         ||    13 || guest checks this feature bit
                                    ||       || before using paravirtualized
                                    ||       || sched yield.