sparc32: fix sparse warning in io-unit.c

Fix following warning:
io-unit.c:56:13: warning: incorrect type in assignment (different address spaces)

The page table for the io unit resides in __iomem.
Fix up all users of the io unit page table.
Introduce sbus helers for all read/write operations.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/arch/sparc/include/asm/io-unit.h b/arch/sparc/include/asm/io-unit.h
index 01ab2f6..04a9701 100644
--- a/arch/sparc/include/asm/io-unit.h
+++ b/arch/sparc/include/asm/io-unit.h
@@ -43,7 +43,7 @@
 struct iounit_struct {
 	unsigned long		bmap[(IOUNIT_DMA_SIZE >> (PAGE_SHIFT + 3)) / sizeof(unsigned long)];
 	spinlock_t		lock;
-	iopte_t			*page_table;
+	iopte_t __iomem		*page_table;
 	unsigned long		rotor[3];
 	unsigned long		limit[4];
 };