gpio: pl061: Support building as module

Enable building the PL061 GPIO driver as a module.

This does change the initcall level when built-in. This shouldn't be a
problem as any user should support deferred probe by now. A scan of DT
based platforms at least didn't reveal any users that would be a
problem.

Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc: linux-gpio@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/Kconfig

@@ -422,7 +422,7 @@ config GPIO_OMAP
 	  Say yes here to enable GPIO support for TI OMAP SoCs.
 
 config GPIO_PL061
-	bool "PrimeCell PL061 GPIO support"
+	tristate "PrimeCell PL061 GPIO support"
 	depends on ARM_AMBA
 	select IRQ_DOMAIN
 	select GPIOLIB_IRQCHIP

drivers/gpio/gpio-pl061.c

@@ -16,6 +16,7 @@
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/irqchip/chained_irq.h>
+#include <linux/module.h>
 #include <linux/bitops.h>
 #include <linux/gpio/driver.h>
 #include <linux/device.h>
@@ -408,6 +409,7 @@ static const struct amba_id pl061_ids[] = {
 	},
 	{ 0, 0 },
 };
+MODULE_DEVICE_TABLE(amba, pl061_ids);
 
 static struct amba_driver pl061_gpio_driver = {
 	.drv = {
@@ -419,9 +421,6 @@ static struct amba_driver pl061_gpio_driver = {
 	.id_table	= pl061_ids,
 	.probe		= pl061_probe,
 };
+module_amba_driver(pl061_gpio_driver);
 
-static int __init pl061_gpio_init(void)
+MODULE_LICENSE("GPL v2");
-{
-	return amba_driver_register(&pl061_gpio_driver);
-}
-device_initcall(pl061_gpio_init);