parisc: hide ioread64 declaration on 32-bit

The definition of ioread64 etc is hidden on 32-bit, but the declaration
remained by accident, which led to the generic definition getting left
out:

ERROR: modpost: "ioread64" [drivers/pci/switch/switchtec.ko] undefined!

Hide the declaration and #define under the same #ifdef.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 77bfc8b ("parisc: Remove 64bit access on 32bit machines")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/parisc/include/asm/io.h

@@ -227,6 +227,7 @@ extern void outsl (unsigned long port, const void *src, unsigned long count);
  * value for either 32 or 64 bit mode */
 #define F_EXTEND(x) ((unsigned long)((x) | (0xffffffff00000000ULL)))
 
+#ifdef CONFIG_64BIT
 #define ioread64 ioread64
 #define ioread64be ioread64be
 #define iowrite64 iowrite64
@@ -235,6 +236,7 @@ extern u64 ioread64(const void __iomem *addr);
 extern u64 ioread64be(const void __iomem *addr);
 extern void iowrite64(u64 val, void __iomem *addr);
 extern void iowrite64be(u64 val, void __iomem *addr);
+#endif
 
 #include <asm-generic/iomap.h>
 /*