ARM: sunxi: add missing include for mdelay()

  CC      arch/arm/mach-sunxi/sunxi.o
./arch/arm/mach-sunxi/sunxi.c: In function 'sunxi_restart':
./arch/arm/mach-sunxi/sunxi.c:55:3: error: implicit declaration of function 'mdelay' [-Werror=implicit-function-declaration]

Signed-off-by: Josh Cartwright <josh.cartwright@ni.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Olof Johansson <olof@lixom.net>