x86/pmu: Snapshot CPUID.0xA PMU capabilities during BSP initialization

Snapshot PMU info from CPUID.0xA into "struct pmu_caps pmu" during
pmu_init() instead of reading CPUID.0xA every time a test wants to query
PMU capabilities.  Using pmu_caps to track various properties will also
make it easier to hide the differences between AMD and Intel PMUs.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221102225110.3023543-17-seanjc@google.com