genirq: Remove CONFIG_IRQ_PER_CPU

The saving of this switch is minimal versus the ifdef mess it
creates. Simple enable PER_CPU unconditionally and remove the config
switch.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/irq/Kconfig

@@ -32,9 +32,6 @@ config GENERIC_PENDING_IRQ
 config AUTO_IRQ_AFFINITY
        def_bool n
 
-config IRQ_PER_CPU
-       def_bool n
-
 config HARDIRQS_SW_RESEND
        def_bool n