[ARM] arch/arm/kernel/isa.c: missing definition of register_isa_ports

arch/arm/kernel/isa.c should include <linux/io.h> to get the
definition of register_io_ports() at-least when compiling for
footbridge to fix the following sparse warning:

isa.c:68:1: warning: symbol 'register_isa_ports' was not declared.
Signed-off-by: NBen Dooks <ben-linux@fluff.org>

arch/arm/kernel/isa.c

@@ -16,6 +16,7 @@
 #include <linux/fs.h>
 #include <linux/sysctl.h>
 #include <linux/init.h>
+#include <linux/io.h>
 
 static unsigned int isa_membase, isa_portbase, isa_portshift;