KVM: x86/pmu: Change ambiguous _mask suffix to _rsvd in kvm_pmu

KVM: x86/pmu: Change ambiguous _mask suffix to _rsvd in kvm_pmu

Several '_mask' suffixed variables such as, global_ctrl_mask, are
defined in kvm_pmu structure. However the _mask suffix is ambiguous and
misleading since it's not a real mask with positive logic. On the contrary
it represents the reserved bits of corresponding MSRs and these bits
should not be accessed.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20240430005239.13527-2-dapeng1.mi@linux.intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>