plic: clear irq pending when init plic

there maybe some irq pending triggered by uboot driver,
the pending will not be cleared even when irq source is
cleared. when the irq source driver devm_request_irq, the
isr will be triggered, but the devm_request_irq is not finished,
and the driver is not ready, there may be some problems.
so, try to clear all irq pending when init plic

Change-Id: I88db4db0af7f7e8a9893b0ffb9db07b7d0203c37

drivers/irqchip/irq-sifive-plic.c

@@ -46,6 +46,7 @@
  * There's one bit for each interrupt source.
  */
 #ifdef CONFIG_SOC_SPACEMIT
+#define PENDING_BASE			0x1000
 #define CONTEXT_ENABLE_BASE		0x2080
 #define CONTEXT_ENABLE_SIZE		0x100
 #else
@@ -573,6 +574,10 @@ static int __init __plic_init(struct device_node *node,
 done:
 		for (hwirq = 1; hwirq <= nr_irqs; hwirq++) {
 			plic_toggle(handler, hwirq, 0);
+			#ifdef CONFIG_SOC_SPACEMIT
+			/* clear pending, which maybe triggered by uboot */
+			writel(0, priv->regs + PENDING_BASE + (hwirq/32)*4);
+			#endif
 			writel(1, priv->regs + PRIORITY_BASE +
 				  hwirq * PRIORITY_PER_ID);
 		}