asm-generic/io.h: convert readX defines to functions

E.g. readl is defined like this

 #define readl(addr) __le32_to_cpu(__raw_readl(addr))

If a there is a readl() call that doesn't check the return value
this will cause a compile warning on big endian machines due to
the __le32_to_cpu macro magic.

E.g. code like this:

	readl(addr);

will generate the following compile warning:

warning: value computed is not used [-Wunused-value]

With this patch we get rid of dozens of compile warnings on s390.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

include/asm-generic/io.h

@@ -53,8 +53,18 @@ static inline u32 __raw_readl(const volatile void __iomem *addr)
 #endif
 
 #define readb __raw_readb
-#define readw(addr) __le16_to_cpu(__raw_readw(addr))
-#define readl(addr) __le32_to_cpu(__raw_readl(addr))
+
+#define readw readw
+static inline u16 readw(const volatile void __iomem *addr)
+{
+	return __le16_to_cpu(__raw_readw(addr));
+}
+
+#define readl readl
+static inline u32 readl(const volatile void __iomem *addr)
+{
+	return __le32_to_cpu(__raw_readl(addr));
+}
 
 #ifndef __raw_writeb
 static inline void __raw_writeb(u8 b, volatile void __iomem *addr)
@@ -89,7 +99,11 @@ static inline u64 __raw_readq(const volatile void __iomem *addr)
 }
 #endif
 
-#define readq(addr) __le64_to_cpu(__raw_readq(addr))
+#define readq readq
+static inline u64 readq(const volatile void __iomem *addr)
+{
+	return __le64_to_cpu(__raw_readq(addr));
+}
 
 #ifndef __raw_writeq
 static inline void __raw_writeq(u64 b, volatile void __iomem *addr)