riscv : add riscv qemu virt support and fix fs bit error in mstatus

ports/risc-v64/gnu/example_build/qemu_virt/plic.c

@@ -0,0 +1,72 @@
+#include "plic.h"
+#include <stddef.h>
+irq_callback callbacks[MAX_CALLBACK_NUM];
+
+void plic_irq_enable(int irqno)
+{
+	int hart = riscv_get_core();
+	*(uint32_t*)PLIC_MENABLE(hart) = (*(uint32_t*)PLIC_MENABLE(hart) | (1 << irqno));
+	return;
+}
+
+void plic_irq_disable(int irqno)
+{
+	int hart = riscv_get_core();
+        *(uint32_t*)PLIC_MENABLE(hart) = (*(uint32_t*)PLIC_MENABLE(hart) & (~(1 << irqno)));
+        return;
+}
+
+void plic_prio_set(int irqno, int prio)
+{
+	PLIC_SET_PRIO(irqno, prio);
+}
+
+int  plic_prio_get(int irqno)
+{
+	return PLIC_GET_PRIO(irqno);
+}
+
+int  plic_register_callback(int irqno, irq_callback callback)
+{
+	if(!(irqno >=0 && irqno < MAX_CALLBACK_NUM))
+		return -1;
+	callbacks[irqno] = callback;
+	return 0;
+}
+
+int  plic_unregister_callback(int irqno)
+{
+	return plic_register_callback(irqno, NULL);
+}
+
+int  plic_init(void)
+{
+	for(int i=0;i<MAX_CALLBACK_NUM;i++)
+	{
+		callbacks[i] = NULL;
+	}
+	return 0;
+}
+
+int  plic_claim(void)
+{
+	int hart = riscv_get_core();
+	return (*(uint32_t*)PLIC_MCLAIM(hart));
+}
+
+void plic_complete(int irqno)
+{
+	int hart = riscv_get_core();
+	*(uint32_t*)(PLIC_MCOMPLETE(hart)) = (uint32_t)irqno;
+	return;
+}
+
+int  plic_irq_intr(void)
+{
+	int ret = -1;
+	int irqno = plic_claim();
+	if(callbacks[irqno] != NULL)
+		ret = (callbacks[irqno])(irqno);
+	plic_complete(irqno);
+	return ret;
+}