arch: rely on asm-generic/io.h for default ioremap_* definitions

Various architectures that use asm-generic/io.h still defined their
own default versions of ioremap_nocache, ioremap_wt and ioremap_wc
that point back to plain ioremap directly or indirectly.  Remove these
definitions and rely on asm-generic/io.h instead.  For this to work
the backup ioremap_* defintions needs to be changed to purely cpp
macros instea of inlines to cover for architectures like openrisc
that only define ioremap after including <asm-generic/io.h>.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Palmer Dabbelt <palmer@dabbelt.com>

arch/nios2/include/asm/io.h

@@ -33,10 +33,6 @@ static inline void iounmap(void __iomem *addr)
 	__iounmap(addr);
 }
 
-#define ioremap_nocache ioremap
-#define ioremap_wc ioremap
-#define ioremap_wt ioremap
-
 /* Pages to physical address... */
 #define page_to_phys(page)	virt_to_phys(page_to_virt(page))