powerpc/kexec: Fix regression causing compile failure on UP

Recent commit b987812b caused
a compile failure on UP because a considerably large block
of the file was included within CONFIG_SMP, hence making a stub
function not exposed on UP builds when it needed to be.

Relocate the stub to the #else /* ! CONFIG_SMP */ section
and also annotate the relevant else/endif so that nobody
else falls into the same trap I did.
Reported-by: Michael Guntsche <mike@it-loops.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/crash.c

@@ -163,7 +163,7 @@ static void crash_kexec_prepare_cpus(int cpu)
 }
 
 /* wait for all the CPUs to hit real mode but timeout if they don't come in */
-#if defined(CONFIG_PPC_STD_MMU_64) && defined(CONFIG_SMP)
+#ifdef CONFIG_PPC_STD_MMU_64
 static void crash_kexec_wait_realmode(int cpu)
 {
 	unsigned int msecs;
@@ -188,9 +188,7 @@ static void crash_kexec_wait_realmode(int cpu)
 	}
 	mb();
 }
-#else
-static inline void crash_kexec_wait_realmode(int cpu) {}
-#endif
+#endif	/* CONFIG_PPC_STD_MMU_64 */
 
 /*
  * This function will be called by secondary cpus or by kexec cpu
@@ -235,7 +233,9 @@ void crash_kexec_secondary(struct pt_regs *regs)
 	crash_ipi_callback(regs);
 }
 
-#else
+#else	/* ! CONFIG_SMP */
+static inline void crash_kexec_wait_realmode(int cpu) {}
+
 static void crash_kexec_prepare_cpus(int cpu)
 {
 	/*
@@ -255,7 +255,7 @@ void crash_kexec_secondary(struct pt_regs *regs)
 {
 	cpus_in_sr = CPU_MASK_NONE;
 }
-#endif
+#endif	/* CONFIG_SMP */
 
 /*
  * Register a function to be called on shutdown.  Only use this if you