target/arm: clear PMUVER field of AA64DFR0 when vPMU=off

The PMUv3 driver of linux kernel (in arch/arm64/kernel/perf_event.c)
relies on the PMUVER field of id_aa64dfr0_el1 to decide if PMU support
is present or not. This patch clears the PMUVER field under TCG mode
when vPMU=off. Without it, PMUv3 will init insider guest VMs even
with vPMU=off. This patch also removes a redundant line inside the
if-statement.
Signed-off-by: NWei Huang <wei@redhat.com>
Message-id: 1495123889-32301-1-git-send-email-wei@redhat.com
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target/arm/cpu.c

@@ -750,8 +750,8 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
     }
 
     if (!cpu->has_pmu) {
-        cpu->has_pmu = false;
         unset_feature(env, ARM_FEATURE_PMU);
+        cpu->id_aa64dfr0 &= ~0xf00;
     }
 
     if (!arm_feature(env, ARM_FEATURE_EL2)) {