KVM: selftests: Add and use KVM helpers for x86 Family and Model

Add KVM variants of the x86 Family and Model helpers, and use them in the
PMU event filter test.  Open code the retrieval of KVM's supported CPUID
entry 0x1.0 in anticipation of dropping kvm_get_supported_cpuid_entry().

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221006005125.680782-12-seanjc@google.com