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 3f6da390 ("perf:
Rework and fix the arch CPU-hotplug hooks")

So, apply same changes as commit 3f6da390 ("perf: Rework and fix
the arch CPU-hotplug hooks") then commit 57ecde42 ("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: 3f6da390 ("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