powerpc/pseries/hibernation: switch to rtas_ibm_suspend_me()

rtas_suspend_last_cpu() and related code perform a lot of work that
isn't relevant to the hibernation workflow. All other CPUs are offline
when called so there is no need to place them in H_JOIN or prod them
on resume, nor is there need for retries or operations on shared
state.

Call the rtas_ibm_suspend_me() wrapper function directly from
pseries_suspend_enter() instead of using rtas_suspend_last_cpu().

Signed-off-by: Nathan Lynch <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/platforms/pseries/suspend.c

···
  **/
 static int pseries_suspend_enter(suspend_state_t state)
 {
-	int rc = rtas_suspend_last_cpu(&suspend_data);
-
-	atomic_set(&suspending, 0);
-	atomic_set(&suspend_data.done, 1);
-	return rc;
+	return rtas_ibm_suspend_me(NULL);
 }
 
 /**