powerpc/perf: Convert fsl_emb notifier to state machine callbacks

  CC      arch/powerpc/perf/core-fsl-emb.o
arch/powerpc/perf/core-fsl-emb.c:675:6: error: no previous prototype for 'hw_perf_event_setup' [-Werror=missing-prototypes]
  675 | void hw_perf_event_setup(int cpu)
      |      ^~~~~~~~~~~~~~~~~~~

Looks like fsl_emb was completely missed by commit 3f6da39 ("perf:
Rework and fix the arch CPU-hotplug hooks")

So, apply same changes as commit 3f6da39 ("perf: Rework and fix
the arch CPU-hotplug hooks") then commit 57ecde4 ("powerpc/perf:
Convert book3s notifier to state machine callbacks")

While at it, also fix following error:

arch/powerpc/perf/core-fsl-emb.c: In function 'perf_event_interrupt':
arch/powerpc/perf/core-fsl-emb.c:648:13: error: variable 'found' set but not used [-Werror=unused-but-set-variable]
  648 |         int found = 0;
      |             ^~~~~

Fixes: 3f6da39 ("perf: Rework and fix the arch CPU-hotplug hooks")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/603e1facb32608f88f40b7d7b9094adc50e7b2dc.1692349125.git.christophe.leroy@csgroup.eu

Author: chleroy

arch/powerpc/perf/core-fsl-emb.c

@@ -645,7 +645,6 @@ static void perf_event_interrupt(struct pt_regs *regs)
 	struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);
 	struct perf_event *event;
 	unsigned long val;
-	int found = 0;
 
 	for (i = 0; i < ppmu->n_counter; ++i) {
 		event = cpuhw->event[i];
@@ -654,7 +653,6 @@ static void perf_event_interrupt(struct pt_regs *regs)
 		if ((int)val < 0) {
 			if (event) {
 				/* event has overflowed */
-				found = 1;
 				record_and_restart(event, val, regs);
 			} else {
 				/*
@@ -672,11 +670,13 @@ static void perf_event_interrupt(struct pt_regs *regs)
 	isync();
 }
 
-void hw_perf_event_setup(int cpu)
+static int fsl_emb_pmu_prepare_cpu(unsigned int cpu)
 {
 	struct cpu_hw_events *cpuhw = &per_cpu(cpu_hw_events, cpu);
 
 	memset(cpuhw, 0, sizeof(*cpuhw));
+
+	return 0;
 }
 
 int register_fsl_emb_pmu(struct fsl_emb_pmu *pmu)
@@ -689,6 +689,8 @@ int register_fsl_emb_pmu(struct fsl_emb_pmu *pmu)
 		pmu->name);
 
 	perf_pmu_register(&fsl_emb_pmu, "cpu", PERF_TYPE_RAW);
+	cpuhp_setup_state(CPUHP_PERF_POWER, "perf/powerpc:prepare",
+			  fsl_emb_pmu_prepare_cpu, NULL);
 
 	return 0;
 }