[S390] pm: fix build error for !SMP

Fix build error for !SMP:

arch/s390/power/built-in.o: In function `swsusp_arch_resume':
(.text+0x1b4): undefined reference to `smp_get_phys_cpu_id'
arch/s390/power/built-in.o: In function `swsusp_arch_resume':
(.text+0x288): undefined reference to `smp_switch_boot_cpu_in_resume'
make: *** [.tmp_vmlinux1] Error 1

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>