powerpc/rcpm: Fix build break when SMP=n

Add an include of asm/smp.h to fix a build break when SMP=n:

  arch/powerpc/sysdev/fsl_rcpm.c:32:2: error: implicit declaration of
  function 'get_hard_smp_processor_id'

Fixes: d17799f9c10e ("powerpc/rcpm: add RCPM driver")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/sysdev/fsl_rcpm.c

@@ -22,6 +22,7 @@
 #include <linux/fsl/guts.h>
 #include <asm/cputhreads.h>
 #include <asm/fsl_pm.h>
+#include <asm/smp.h>
 
 static struct ccsr_rcpm_v1 __iomem *rcpm_v1_regs;
 static struct ccsr_rcpm_v2 __iomem *rcpm_v2_regs;