KVM: x86/pmu: Add wrappers for counting emulated instructions/branches

KVM: x86/pmu: Add wrappers for counting emulated instructions/branches

Add wrappers for triggering instruction retired and branch retired PMU
events in anticipation of reworking the internal mechanisms to track
which PMCs need to be evaluated, e.g. to avoid having to walk and check
every PMC.

Opportunistically bury "struct kvm_pmu_emulated_event_selectors" in pmu.c.

No functional change intended.

Link: https://lore.kernel.org/r/20250805190526.1453366-11-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>