powerpc/85xx: Fix no previous prototype warning for mpc85xx_setup_pmc()

Fixes the following W=1 warning:
  arch/powerpc/platforms/85xx/mpc85xx_pm_ops.c:89:12: warning: no previous prototype for 'mpc85xx_setup_pmc'
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211124093254.1054750-1-mpe@ellerman.id.au

arch/powerpc/platforms/85xx/mpc85xx_pm_ops.c

@@ -15,6 +15,8 @@
 #include <asm/io.h>
 #include <asm/fsl_pm.h>
 
+#include "smp.h"
+
 static struct ccsr_guts __iomem *guts;
 
 #ifdef CONFIG_FSL_PMC