gpio: Add missing plat header

platsupport/plat/gpio.h was removed from the arch interface and must be
included by the caller.

libusbdrivers/src/plat/exynos5/ehci-exynos5.c

diff --git a/libusbdrivers/src/plat/exynos5/ehci-exynos5.c b/libusbdrivers/src/plat/exynos5/ehci-exynos5.c
index 362ed69..51547ed 100644
--- a/libusbdrivers/src/plat/exynos5/ehci-exynos5.c
+++ b/libusbdrivers/src/plat/exynos5/ehci-exynos5.c
@@ -11,6 +11,7 @@
  */
 #include <platsupport/clock.h>
 #include <platsupport/gpio.h>
+#include <platsupport/plat/gpio.h>
 #include <platsupport/mach/pmic.h>
 #include <platsupport/plat/sysreg.h>
 #include <usb/usb_host.h>