KVM: x86/pmu: Refactor PERF_GLOBAL_CTRL update helper for reuse by PEBS

KVM: x86/pmu: Refactor PERF_GLOBAL_CTRL update helper for reuse by PEBS

Extract the "global ctrl" specific bits out of global_ctrl_changed() so
that the helper only deals with reprogramming general purpose counters,
and rename the helper accordingly.  PEBS needs the same logic, i.e needs
to reprogram counters associated when PEBS_ENABLE bits are toggled, and
will use the helper in a future fix.

No functional change intended.

Signed-off-by: Like Xu <likexu@tencent.com>
Link: https://lore.kernel.org/r/20220831085328.45489-4-likexu@tencent.com
[sean: split to separate patch, write changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>