KVM: x86: Update comments about MSR lists exposed to userspace

KVM: x86: Update comments about MSR lists exposed to userspace

Refresh comments about msrs_to_save, emulated_msrs, and msr_based_features
to remove stale references left behind by commit 2374b7310b66 (KVM:
x86/pmu: Use separate array for defining "PMU MSRs to save"), and to
better reflect the current reality, e.g. emulated_msrs is no longer just
for MSRs that are "kvm-specific".

Reported-by: Binbin Wu <binbin.wu@linux.intel.com>
Link: https://lore.kernel.org/r/20230607004636.1421424-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>