KVM: selftests: Update top-of-file comment in psci_test

Fix the comment to accurately describe the test and recently added
SYSTEM_SUSPEND test case.

What was once psci_cpu_on_test was renamed and extended to squeeze in a
test case for PSCI SYSTEM_SUSPEND. Nonetheless, the author of those
changes (whoever they may be...) failed to update the file comment to
reflect what had changed.
Reported-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220819162100.213854-1-oliver.upton@linux.dev

tools/testing/selftests/kvm/aarch64/psci_test.c

 // SPDX-License-Identifier: GPL-2.0-only
 /*
- * psci_cpu_on_test - Test that the observable state of a vCPU targeted by the
- * CPU_ON PSCI call matches what the caller requested.
+ * psci_test - Tests relating to KVM's PSCI implementation.
  *
  * Copyright (c) 2021 Google LLC.
  *
- * This is a regression test for a race between KVM servicing the PSCI call and
- * userspace reading the vCPUs registers.
+ * This test includes:
+ *  - A regression test for a race between KVM servicing the PSCI CPU_ON call
+ *    and userspace reading the targeted vCPU's registers.
+ *  - A test for KVM's handling of PSCI SYSTEM_SUSPEND and the associated
+ *    KVM_SYSTEM_EVENT_SUSPEND UAPI.
  */
 
 #define _GNU_SOURCE