[PATCH] powerpc/8xx: Fix m8xx_wdt issues

The following fixes some issues with the last mpc8xx_wdt update:

- Adds missing #include <asm/io.h>
- Use "uint __iomem" pointer for in_be32/out_be32

Signed-off-by: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>