sh: irqstat: Use the generic irq_cpustat_t

SH can now use the generic irq_cpustat_t. Define ack_bad_irq so the generic
header does not emit the generic version of it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20201113141733.625146223@linutronix.de