KVM: x86: Use static calls to reduce kvm_pmu_ops overhead

Use static calls to improve kvm_pmu_ops performance, following the same
pattern and naming scheme used by kvm-x86-ops.h.

Here are the worst fenced_rdtsc() cycles numbers for the kvm_pmu_ops
functions that is most often called (up to 7 digits of calls) when running
a single perf test case in a guest on an ICX 2.70GHz host (mitigations=on):

		|	legacy	|	static call
------------------------------------------------------------
.pmc_idx_to_pmc	|	1304840	|	994872 (+23%)
.pmc_is_enabled	|	978670	|	1011750 (-3%)
.msr_idx_to_pmc	|	47828	|	41690 (+12%)
.is_valid_msr	|	28786	|	30108 (-4%)

Signed-off-by: Like Xu <likexu@tencent.com>
[sean: Handle static call updates in pmu.c, tweak changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220329235054.3534728-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>