powerpc/kexec: Fix build failure on 32-bit SMP

powerpc/kexec: Fix build failure on 32-bit SMP

Commit aaae2aff4516005b781b84d7cc649b656a1de133 left
crash_kexec_wait_realmode() undefined for UP.

Commit 778db0d44256ef3bdb043d131bed57e8c60d0560 defined it for UP but
left it undefined for 32-bit SMP.

Seems like people are getting confused by nested #ifdef's, so move the
definitions of crash_kexec_wait_realmode() after the #ifdef CONFIG_SMP
section.

Compile-tested with 32-bit UP, 32-bit SMP and 64-bit SMP configurations.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Tested-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>