powerpc/xmon: Add __init attribute to eligible functions

`xmon_register_spus` defined in 'arch/powerpc/xmon' is deserving of an
`__init` macro attribute. This functions is only called by other
initialization functions and therefore should inherit the attribute.
Also, change the function declaration in the header file to include
`__init`.
Signed-off-by: Nick Child <nick.child@ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211216220035.605465-7-nick.child@ibm.com

arch/powerpc/include/asm/xmon.h

@@ -12,7 +12,7 @@
 
 #ifdef CONFIG_XMON
 extern void xmon_setup(void);
-extern void xmon_register_spus(struct list_head *list);
+void __init xmon_register_spus(struct list_head *list);
 struct pt_regs;
 extern int xmon(struct pt_regs *excp);
 extern irqreturn_t xmon_irq(int, void *);

arch/powerpc/xmon/xmon.c

@@ -4136,7 +4136,7 @@ struct spu_info {
 
 static struct spu_info spu_info[XMON_NUM_SPUS];
 
-void xmon_register_spus(struct list_head *list)
+void __init xmon_register_spus(struct list_head *list)
 {
 	struct spu *spu;