arm: vt8500: Fixup for missing gpio.h

mach/include/gpio.h was removed as part of the multiplatform-3.7
update. This patch removes the include from arch-vt8500/vt8500.c

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
Signed-off-by: Olof Johansson <olof@lixom.net>