powerpc: Pull common bits of setup_{32,64}.c into setup-common.c

This creates a new arch/powerpc/kernel/setup-common.c with various
bits that setup_32.c and setup_64.c had in common - functions like
machine_shutdown/restart/power_off, show_cpuinfo, set_preferred_console
etc.

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index eaedb7e..3010176 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -32,7 +32,7 @@
 extra-y				+= vmlinux.lds
 
 obj-y				+= process.o init_task.o time.o \
-				   prom.o systbl.o traps.o
+				   prom.o systbl.o traps.o setup-common.o
 obj-$(CONFIG_PPC32)		+= entry_32.o idle_6xx.o setup_32.o misc_32.o
 obj-$(CONFIG_PPC64)		+= setup_64.o misc_64.o
 obj-$(CONFIG_PPC_OF)		+= prom_init.o