target/i386/kvm: set KVM_PMU_CAP_DISABLE if "-pmu" is configured

target/i386/kvm: set KVM_PMU_CAP_DISABLE if "-pmu" is configured

Although AMD PERFCORE and PerfMonV2 are removed when "-pmu" is configured,
there is no way to fully disable KVM AMD PMU virtualization. Neither
"-cpu host,-pmu" nor "-cpu EPYC" achieves this.

As a result, the following message still appears in the VM dmesg:

[    0.263615] Performance Events: AMD PMU driver.

However, the expected output should be:

[    0.596381] Performance Events: PMU not available due to virtualization, using software events only.
[    0.600972] NMI watchdog: Perf NMI watchdog permanently disabled

This occurs because AMD does not use any CPUID bit to indicate PMU
availability.

To address this, KVM_CAP_PMU_CAPABILITY is used to set KVM_PMU_CAP_DISABLE
when "-pmu" is configured.

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Reviewed-by: Zide Chen <zide.chen@intel.com>
Link: https://lore.kernel.org/r/20260109075508.113097-2-dongli.zhang@oracle.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>