gpio: sim: add missing include

We use size_t, ssize_t, bool and some other types defined in
linux/types.h so include it in the driver.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

drivers/gpio/gpio-sim.c

@@ -31,6 +31,7 @@
 #include <linux/string.h>
 #include <linux/string_helpers.h>
 #include <linux/sysfs.h>
+#include <linux/types.h>
 
 #define GPIO_SIM_NGPIO_MAX	1024
 #define GPIO_SIM_PROP_MAX	4 /* Max 3 properties + sentinel. */