[PATCH] Fix broken initialization of conswitchp for ARCH=ppc64

In the merge tree, commit 0458060c
broke boot on some machines because the initialization of conswitchp
was moved to arch/powerpc/kernel/setup_64.c, but a corresponding copy
was not added to arch/ppc64/kernel/setup.c.  This patch fixes it.

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>