perf/x86/uncore: Fix potential NULL pointer in uncore_get_alias_name

The current code assumes that the discovery table provides valid
box_ids for the normal units. It's not the case anymore since some units
in the discovery table are broken on some SPR variants.

Factor out uncore_get_box_id(). Check the existence of the type->box_ids
before using it. If it's not available, use pmu_idx.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Michael Petlan <mpetlan@redhat.com>
Link: https://lore.kernel.org/r/20230112200105.733466-3-kan.liang@linux.intel.com