gpio: don't include module.h in shared driver header

Most shared headers in include/linux don't need to know what the
internals of a struct module are; all they care about is that it
is a struct and hence they may require a pointer to one.

The advantage in this is that module.h is including a lot of stuff
itself, and an otherwise empty C file that just contains module.h
will result in ~750kB from CPP (compared to say 12kB from init.h)

So we have approximately 50 instances of "struct module;" in the
various include/linux headers already that help us keep module.h
out of other headers; here we do the same for gpio.

Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: linux-gpio@vger.kernel.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/gpio/driver.h

@@ -3,7 +3,6 @@
 
 #include <linux/device.h>
 #include <linux/types.h>
-#include <linux/module.h>
 #include <linux/irq.h>
 #include <linux/irqchip/chained_irq.h>
 #include <linux/irqdomain.h>
@@ -16,6 +15,7 @@ struct of_phandle_args;
 struct device_node;
 struct seq_file;
 struct gpio_device;
+struct module;
 
 #ifdef CONFIG_GPIOLIB