ARM: shmobile: don't call platform_can_secondary_boot on UP

For rcar-gen2, we build the SMP files even for UP configurations,
and that just broke:

arch/arm/mach-shmobile/built-in.o: In function `shmobile_smp_init_fallback_ops':
pm-rcar-gen2.c:(.init.text+0x40c): undefined reference to `platform_can_secondary_boot'

This adds an compile-time check before the call to platform_can_secondary_boot,
turning the function into an empty stub for UP configurations.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: c21af444 ("ARM: shmobile: smp: Add function to prioritize DT SMP")
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Olof Johansson <olof@lixom.net>

arch/arm/mach-shmobile/platsmp.c

@@ -40,5 +40,8 @@ bool shmobile_smp_cpu_can_disable(unsigned int cpu)
 bool __init shmobile_smp_init_fallback_ops(void)
 {
 	/* fallback on PSCI/smp_ops if no other DT based method is detected */
+	if (!IS_ENABLED(CONFIG_SMP))
+		return false;
+
 	return platform_can_secondary_boot() ? true : false;
 }