serial: sh-sci: Provide a helper for muxed IRQs.

All of the muxed IRQs presently populate the IRQ array verbosely, this
simply provides a trivial helper to do it for them.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

include/linux/serial_sci.h

@@ -34,6 +34,14 @@ enum {
 	SCIx_NR_IRQS,
 };
 
+#define SCIx_IRQ_MUXED(irq)		\
+{					\
+	[SCIx_ERI_IRQ]	= (irq),	\
+	[SCIx_RXI_IRQ]	= (irq),	\
+	[SCIx_TXI_IRQ]	= (irq),	\
+	[SCIx_BRI_IRQ]	= (irq),	\
+}
+
 struct device;
 
 /*