KVM: selftests: Add pmu.h and lib/pmu.c for common PMU assets

Add a PMU library for x86 selftests to help eliminate open-coded event
encodings, and to reduce the amount of copy+paste between PMU selftests.

Use the new common macro definitions in the existing PMU event filter test.

Cc: Aaron Lewis <aaronlewis@google.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Jinrong Liang <cloudliang@tencent.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20240109230250.424295-16-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>