KVM: x86/pmu: Add macros to iterate over all PMCs given a bitmap

Add and use kvm_for_each_pmc() to dedup a variety of open coded for-loops
that iterate over valid PMCs given a bitmap (and because seeing checkpatch
whine about bad macro style is always amusing).

No functional change intended.

Link: https://lore.kernel.org/r/20231110022857.1273836-6-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>