sched: Make PELT acronym definition searchable

The PELT acronym definition can be found right at the top of
kernel/sched/pelt.c (of course), but it cannot be found through use of

grep -r PELT kernel/sched/

Add the acronym "(PELT)" after "Per Entity Load Tracking" at the top of
the source file.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20231012125824.1260774-1-mathieu.desnoyers@efficios.com

kernel/sched/pelt.c

 // SPDX-License-Identifier: GPL-2.0
 /*
- * Per Entity Load Tracking
+ * Per Entity Load Tracking (PELT)
  *
  *  Copyright (C) 2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  *