PM: Add empty suspend/resume device irq functions

git commit 0a0c5168 "PM: Introduce functions for suspending and resuming
device interrupts" introduced some helper functions. However these
functions are only available for architectures which support
GENERIC_HARDIRQS.

Other architectures will see this build error:

drivers/built-in.o: In function `sysdev_suspend':
(.text+0x15138): undefined reference to `check_wakeup_irqs'
drivers/built-in.o: In function `device_power_up':
(.text+0x1cb66): undefined reference to `resume_device_irqs'
drivers/built-in.o: In function `device_power_down':
(.text+0x1cb92): undefined reference to `suspend_device_irqs'

To fix this add some empty inline functions for !GENERIC_HARDIRQS.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

include/linux/interrupt.h

@@ -183,6 +183,7 @@ extern void disable_irq(unsigned int irq);
 extern void enable_irq(unsigned int irq);
 
 /* The following three functions are for the core kernel use only. */
+#ifdef CONFIG_GENERIC_HARDIRQS
 extern void suspend_device_irqs(void);
 extern void resume_device_irqs(void);
 #ifdef CONFIG_PM_SLEEP
@@ -190,6 +191,11 @@ extern int check_wakeup_irqs(void);
 #else
 static inline int check_wakeup_irqs(void) { return 0; }
 #endif
+#else
+static inline void suspend_device_irqs(void) { };
+static inline void resume_device_irqs(void) { };
+static inline int check_wakeup_irqs(void) { return 0; }
+#endif
 
 #if defined(CONFIG_SMP) && defined(CONFIG_GENERIC_HARDIRQS)