irqchip/renesas-rzg2l: Add macro to retrieve TITSR register offset based on register's index

There are 2 TITSR registers available on the IA55 interrupt controller.

Add a macro that retrieves the TITSR register offset based on it's
index. This macro is useful in when adding suspend/resume support so both
TITSR registers can be accessed in a for loop.
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20231120111820.87398-7-claudiu.beznea.uj@bp.renesas.com

drivers/irqchip/irq-renesas-rzg2l.c

@@ -28,8 +28,7 @@
 #define ISCR				0x10
 #define IITSR				0x14
 #define TSCR				0x20
-#define TITSR0				0x24
-#define TITSR1				0x28
+#define TITSR(n)			(0x24 + (n) * 4)
 #define TITSR0_MAX_INT			16
 #define TITSEL_WIDTH			0x2
 #define TSSR(n)				(0x30 + ((n) * 4))
@@ -200,8 +199,7 @@ static int rzg2l_tint_set_edge(struct irq_data *d, unsigned int type)
 	struct rzg2l_irqc_priv *priv = irq_data_to_priv(d);
 	unsigned int hwirq = irqd_to_hwirq(d);
 	u32 titseln = hwirq - IRQC_TINT_START;
-	u32 offset;
-	u8 sense;
+	u8 index, sense;
 	u32 reg;
 
 	switch (type & IRQ_TYPE_SENSE_MASK) {
@@ -217,17 +215,17 @@ static int rzg2l_tint_set_edge(struct irq_data *d, unsigned int type)
 		return -EINVAL;
 	}
 
-	offset = TITSR0;
+	index = 0;
 	if (titseln >= TITSR0_MAX_INT) {
 		titseln -= TITSR0_MAX_INT;
-		offset = TITSR1;
+		index = 1;
 	}
 
 	raw_spin_lock(&priv->lock);
-	reg = readl_relaxed(priv->base + offset);
+	reg = readl_relaxed(priv->base + TITSR(index));
 	reg &= ~(IRQ_MASK << (titseln * TITSEL_WIDTH));
 	reg |= sense << (titseln * TITSEL_WIDTH);
-	writel_relaxed(reg, priv->base + offset);
+	writel_relaxed(reg, priv->base + TITSR(index));
 	raw_spin_unlock(&priv->lock);
 
 	return 0;