KVM: vmx/pmu: Expose LBR_FMT in the MSR_IA32_PERF_CAPABILITIES

Userspace could enable guest LBR feature when the exactly supported
LBR format value is initialized to the MSR_IA32_PERF_CAPABILITIES
and the LBR is also compatible with vPMU version and host cpu model.

The LBR could be enabled on the guest if host perf supports LBR
(checked via x86_perf_get_lbr()) and the vcpu model is compatible
with the host one.

Signed-off-by: Like Xu <like.xu@linux.intel.com>
Message-Id: <20210201051039.255478-11-like.xu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>