h8300: Add missing include file to asm/io.h

h8300 builds fail with

arch/h8300/include/asm/io.h:9:15: error: unknown type name ‘u8’
arch/h8300/include/asm/io.h:15:15: error: unknown type name ‘u16’
arch/h8300/include/asm/io.h:21:15: error: unknown type name ‘u32’

and many related errors.

Fixes: 23c82d41bdf4 ("kexec-allow-architectures-to-override-boot-mapping-fix")
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>