ARM: 6969/1: plat-iop: fix build error

The iop13xx_defconfig didn't build since the platform code uses
defines from <asm/ptrace.h>. Simply add the include so it
compiles.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>