nios2: remove include asm-generic/iomap.h from io.h

Don't need asm-generic/iomap.h and asm-generic/io.h added
default ioread8/16/32 iowrite8/16/32 implementation.
Signed-off-by: Ley Foon Tan <lftan@altera.com>

arch/nios2/include/asm/io.h

@@ -12,7 +12,6 @@
 #define _ASM_NIOS2_IO_H
 
 #include <asm/pgtable-bits.h>
-#include <asm-generic/iomap.h>
 
 /* PCI is not supported in nios2, set this to 0. */
 #define IO_SPACE_LIMIT 0