powerpc: Make ppc_md.{halt, restart} __noreturn

powernv marks it's halt and restart calls as __noreturn. However,
ppc_md does not have this annotation. Add the annotation to ppc_md,
and then to every halt/restart function that is missing it.

Additionally, I have verified that all of these functions do not
return. Occasionally I have added a spin loop to be sure.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/include/asm/machdep.h b/arch/powerpc/include/asm/machdep.h
index 6bdcd0d..a9af1bd 100644
--- a/arch/powerpc/include/asm/machdep.h
+++ b/arch/powerpc/include/asm/machdep.h
@@ -111,8 +111,8 @@
 	/* To setup PHBs when using automatic OF platform driver for PCI */
 	int		(*pci_setup_phb)(struct pci_controller *host);
 
-	void		(*restart)(char *cmd);
-	void		(*halt)(void);
+	void __noreturn	(*restart)(char *cmd);
+	void __noreturn (*halt)(void);
 	void		(*panic)(char *str);
 	void		(*cpu_die)(void);