linux/io.h: import generic ioread* / iowrite* accessors from Linux

Some drivers in Linux (ex. drivers/mtd/nand/denali.c) use
ioread*/iowrite* accessors.  Import them to make drivers more
synced.  I copied code from include/asm-generic/io.h of Linux.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

include/linux/io.h

@@ -9,6 +9,50 @@
 #include <linux/types.h>
 #include <asm/io.h>
 
+static inline u8 ioread8(const volatile void __iomem *addr)
+{
+	return readb(addr);
+}
+
+static inline u16 ioread16(const volatile void __iomem *addr)
+{
+	return readw(addr);
+}
+
+static inline u32 ioread32(const volatile void __iomem *addr)
+{
+	return readl(addr);
+}
+
+#ifdef CONFIG_64BIT
+static inline u64 ioread64(const volatile void __iomem *addr)
+{
+	return readq(addr);
+}
+#endif /* CONFIG_64BIT */
+
+static inline void iowrite8(u8 value, volatile void __iomem *addr)
+{
+	writeb(value, addr);
+}
+
+static inline void iowrite16(u16 value, volatile void __iomem *addr)
+{
+	writew(value, addr);
+}
+
+static inline void iowrite32(u32 value, volatile void __iomem *addr)
+{
+	writel(value, addr);
+}
+
+#ifdef CONFIG_64BIT
+static inline void iowrite64(u64 value, volatile void __iomem *addr)
+{
+	writeq(value, addr);
+}
+#endif /* CONFIG_64BIT */
+
 #ifndef CONFIG_HAVE_ARCH_IOREMAP
 static inline void __iomem *ioremap(resource_size_t offset,
 				    resource_size_t size)