nios2: convert ioremap to use dm cpu data

Convert ioremap() to use io_region_base in dm cpu global data.

Also remove three unused io functions, which have style issue
and are replaced by macros already.
Signed-off-by: NThomas Chou <thomas@wytron.com.tw>

arch/nios2/include/asm/io.h

@@ -44,13 +44,10 @@ static inline phys_addr_t virt_to_phys(void * vaddr)
 
 static inline void *ioremap(unsigned long physaddr, unsigned long size)
 {
-	return (void *)(IO_REGION_BASE | physaddr);
+	DECLARE_GLOBAL_DATA_PTR;
+	return (void *)(gd->arch.io_region_base | physaddr);
 }
 
-extern unsigned char inb (unsigned char *port);
-extern unsigned short inw (unsigned short *port);
-extern unsigned inl (unsigned port);
-
 #define __raw_writeb(v,a)       (*(volatile unsigned char  *)(a) = (v))
 #define __raw_writew(v,a)       (*(volatile unsigned short *)(a) = (v))
 #define __raw_writel(v,a)       (*(volatile unsigned int   *)(a) = (v))