gpio: mxc: Support module build

Change config to tristate, add module device table, module author,
description and license to support module build for i.MX GPIO driver.

As this is a SoC GPIO module, it provides common functions for most
of the peripheral devices, such as GPIO pins control, secondary
interrupt controller for GPIO pins IRQ etc., without GPIO driver, most
of the peripheral devices will NOT work properly, so GPIO module is
similar with clock, pinctrl driver that should be loaded ONCE and
never unloaded.

Since MXC GPIO driver needs to have init function to register syscore
ops once, here still use subsys_initcall(), NOT module_platform_driver().
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Link: https://lore.kernel.org/r/1600320829-1453-1-git-send-email-Anson.Huang@nxp.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/Kconfig

@@ -397,7 +397,7 @@ config GPIO_MVEBU
 	select REGMAP_MMIO
 
 config GPIO_MXC
-	def_bool y
+	tristate "i.MX GPIO support"
 	depends on ARCH_MXC || COMPILE_TEST
 	select GPIO_GENERIC
 	select GENERIC_IRQ_CHIP

drivers/gpio/gpio-mxc.c

@@ -15,6 +15,7 @@
 #include <linux/irq.h>
 #include <linux/irqdomain.h>
 #include <linux/irqchip/chained_irq.h>
+#include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/slab.h>
 #include <linux/syscore_ops.h>
@@ -158,6 +159,7 @@ static const struct of_device_id mxc_gpio_dt_ids[] = {
 	{ .compatible = "fsl,imx7d-gpio", .data = &mxc_gpio_devtype[IMX35_GPIO], },
 	{ /* sentinel */ }
 };
+MODULE_DEVICE_TABLE(of, mxc_gpio_dt_ids);
 
 /*
  * MX2 has one interrupt *for all* gpio ports. The list is used
@@ -604,3 +606,7 @@ static int __init gpio_mxc_init(void)
 	return platform_driver_register(&mxc_gpio_driver);
 }
 subsys_initcall(gpio_mxc_init);
+
+MODULE_AUTHOR("Shawn Guo <shawn.guo@linaro.org>");
+MODULE_DESCRIPTION("i.MX GPIO Driver");
+MODULE_LICENSE("GPL");