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/platforms/embedded6xx/gamecube.c b/arch/powerpc/platforms/embedded6xx/gamecube.c
index fe0ed6e..b17705c 100644
--- a/arch/powerpc/platforms/embedded6xx/gamecube.c
+++ b/arch/powerpc/platforms/embedded6xx/gamecube.c
@@ -29,14 +29,14 @@
 #include "usbgecko_udbg.h"
 
 
-static void gamecube_spin(void)
+static void __noreturn gamecube_spin(void)
 {
 	/* spin until power button pressed */
 	for (;;)
 		cpu_relax();
 }
 
-static void gamecube_restart(char *cmd)
+static void __noreturn gamecube_restart(char *cmd)
 {
 	local_irq_disable();
 	flipper_platform_reset();
@@ -49,7 +49,7 @@
 	gamecube_spin();
 }
 
-static void gamecube_halt(void)
+static void __noreturn gamecube_halt(void)
 {
 	gamecube_restart(NULL);
 }