[POWERPC] Make kexec_setup() a regular initcall

There's no reason kexec_setup() needs to be called explicitly from
setup_system(), it can just be a regular initcall.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/setup_64.c

@@ -350,10 +350,6 @@ void __init setup_system(void)
 	 */
 	unflatten_device_tree();
 
-#ifdef CONFIG_KEXEC
-	kexec_setup();	/* requires unflattened device tree. */
-#endif
-
 	/*
 	 * Fill the ppc64_caches & systemcfg structures with informations
 	 * retrieved from the device-tree. Need to be called before