gpio: omap: Allow building as a loadable module

We currently get all kinds of errors building the omap gpio driver
as a module starting with:

undefined reference to `omap2_gpio_resume_after_idle'
undefined reference to `omap2_gpio_prepare_for_idle'
...

Let's fix the issue by adding inline functions to the header.
Note that we can now also remove the two unused functions for
omap_set_gpio_debounce and omap_set_gpio_debounce_time.

Then doing rmmod on the module produces further warnings
because of missing exit related functions. Let's add those.

And finally, we can make the Kconfig entry just a tristate
option that's selected for omaps.

Cc: Javier Martinez Canillas <[e-mail]>
Cc: Kevin Hilman <[e-mail]>
Cc: Nishanth Menon <[e-mail]>
Signed-off-by: Tony Lindgren <[e-mail]>
Reviewed-by: Grygorii Strashko <[e-mail]>
Acked-by: Santosh Shilimkar <[e-mail]>
Reviewed-by: Felipe Balbi <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/gpio/Kconfig

···
 	  family of SOCs.
 
 config GPIO_OMAP
-	bool "TI OMAP GPIO support" if COMPILE_TEST && !ARCH_OMAP2PLUS
+	tristate "TI OMAP GPIO support" if ARCH_OMAP2PLUS || COMPILE_TEST
 	default y if ARCH_OMAP
 	depends on ARM
 	select GENERIC_IRQ_CHIP

drivers/gpio/gpio-omap.c

···
 	return 0;
 }
 
+static int omap_gpio_remove(struct platform_device *pdev)
+{
+	struct gpio_bank *bank = platform_get_drvdata(pdev);
+
+	list_del(&bank->node);
+	gpiochip_remove(&bank->chip);
+	pm_runtime_disable(bank->dev);
+
+	return 0;
+}
+
 #ifdef CONFIG_ARCH_OMAP2PLUS
 
 #if defined(CONFIG_PM)
···
 }
 #endif /* CONFIG_PM */
 
+#if IS_BUILTIN(CONFIG_GPIO_OMAP)
 void omap2_gpio_prepare_for_idle(int pwr_mode)
 {
 	struct gpio_bank *bank;
···
 		pm_runtime_get_sync(bank->dev);
 	}
 }
+#endif
 
 #if defined(CONFIG_PM)
 static void omap_gpio_init_context(struct gpio_bank *p)
···
 
 static struct platform_driver omap_gpio_driver = {
 	.probe		= omap_gpio_probe,
+	.remove		= omap_gpio_remove,
 	.driver		= {
 		.name	= "omap_gpio",
 		.pm	= &gpio_pm_ops,
···
 	return platform_driver_register(&omap_gpio_driver);
 }
 postcore_initcall(omap_gpio_drv_reg);
+
+static void __exit omap_gpio_exit(void)
+{
+	platform_driver_unregister(&omap_gpio_driver);
+}
+module_exit(omap_gpio_exit);
+
+MODULE_DESCRIPTION("omap gpio driver");
+MODULE_ALIAS("platform:gpio-omap");
+MODULE_LICENSE("GPL v2");

include/linux/platform_data/gpio-omap.h

···
 	int (*get_context_loss_count)(struct device *dev);
 };
 
+#if IS_BUILTIN(CONFIG_GPIO_OMAP)
 extern void omap2_gpio_prepare_for_idle(int off_mode);
 extern void omap2_gpio_resume_after_idle(void);
-extern void omap_set_gpio_debounce(int gpio, int enable);
-extern void omap_set_gpio_debounce_time(int gpio, int enable);
+#else
+static inline void omap2_gpio_prepare_for_idle(int off_mode)
+{
+}
+
+static inline void omap2_gpio_resume_after_idle(void)
+{
+}
+#endif
 
 #endif