ARM: add missing system_misc.h include to process.c

arm_pm_restart(), arm_pm_idle() and soft_restart() are all declared in system_misc.h, but this file is not included in process.c. Add this missing include. Found via sparse:

arch/arm/kernel/process.c:98:6: warning: symbol 'soft_restart' was not declared. Should it be static? arch/arm/kernel/process.c:127:6: warning: symbol 'arm_pm_restart' was not declared. Should it be static? arch/arm/kernel/process.c:134:6: warning: symbol 'arm_pm_idle' was not declared. Should it be static?

---
 arch/arm/kernel/process.c | 1 +
 1 file changed, 1 insertion(+)

index 204f7d273319..b5444731dbb4 100644
@@ -39,6 +39,7 @@
 #include <asm/processor.h>
 #include <asm/thread_notify.h>
 #include <asm/stacktrace.h>
+#include <asm/system_misc.h>
 #include <asm/mach/time.h>
 #include <asm/tls.h>
 

1.8.3.1