xtensa: use physical addresses for bus addresses

Define virt_to_bus and bus_to_virt as virt_to_phys, and phys_to_virt,
respectively.

Signed-off-by: Chris Zankel <[e-mail]>

arch/xtensa/include/asm/io.h

···
 static inline void iounmap(volatile void __iomem *addr)
 {
 }
+
+#define virt_to_bus     virt_to_phys
+#define bus_to_virt     phys_to_virt
+
 #endif /* CONFIG_MMU */
 
 /*