perf/x86/intel/cstate: Cleanup duplicate attr_groups

The events of the cstate_core and cstate_pkg PMU have the same format.
They both need to create a "events" group (with empty attrs). The
attr_groups can be shared.

Remove the dedicated attr_groups for each cstate PMU. Use the shared
cstate_attr_groups to replace.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20231116142245.1233485-1-kan.liang@linux.intel.com