kvm: Clear performance monitoring CPUID flags

kvm: Clear performance monitoring CPUID flags

Commit 3d446cf17faefd621c0842b58c92a50bd307eec7 ("kvm__setup_cpuid: use
KVM_GET_SUPPORTED_CPUID to simplify cpuid setup") causes the following errors
to be printed on host kernel dmesg:

[  775.134693] kvm: 2882: cpu0 unhandled rdmsr: 0x345
[  775.143130] kvm: 2882: cpu0 unhandled wrmsr: 0x40 data 0
[  775.143136] kvm: 2882: cpu0 unhandled wrmsr: 0x60 data 0
[  775.143141] kvm: 2882: cpu0 unhandled wrmsr: 0x41 data 0
[  775.143146] kvm: 2882: cpu0 unhandled wrmsr: 0x61 data 0
[  775.143150] kvm: 2882: cpu0 unhandled wrmsr: 0x42 data 0
[  775.143155] kvm: 2882: cpu0 unhandled wrmsr: 0x62 data 0
[  775.143159] kvm: 2882: cpu0 unhandled wrmsr: 0x43 data 0
[  775.143164] kvm: 2882: cpu0 unhandled wrmsr: 0x63 data 0

As explained by Cyrill Gorcunov, these MSR accesses come from Linux performance
events subsystems which is not supported by our little hypervisor. Therefore,
clear the performance monitoring CPUID flags to let guest kernels know about
that.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>