nios2: fix virt_to_phys for nios2 with MMU

As the virtual address and physical address mapping of nios2 with
MMU are different. Add a check of MMU, and fix the mapping.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Acked-by: Marek Vasut <marex@denx.de>
Reviewed-by: Ley Foon Tan <lftan@altera.com>

arch/nios2/include/asm/io.h

@@ -39,7 +39,11 @@ static inline void unmap_physmem(void *vaddr, unsigned long flags)
 
 static inline phys_addr_t virt_to_phys(void * vaddr)
 {
-	return (phys_addr_t)(vaddr);
+	DECLARE_GLOBAL_DATA_PTR;
+	if (gd->arch.has_mmu)
+		return (phys_addr_t)vaddr & 0x1fffffff;
+	else
+		return (phys_addr_t)vaddr & 0x7fffffff;
 }
 
 static inline void *ioremap(unsigned long physaddr, unsigned long size)