gpio: sifive: Allow building the driver as a module

This can reduce the kernel image size in multiplatform configurations.

Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

drivers/gpio/Kconfig

@@ -564,7 +564,7 @@ config GPIO_SAMA5D2_PIOBU
 	  maintain their value during backup/self-refresh.
 
 config GPIO_SIFIVE
-	bool "SiFive GPIO support"
+	tristate "SiFive GPIO support"
 	depends on OF_GPIO
 	select IRQ_DOMAIN_HIERARCHY
 	select GPIO_GENERIC

drivers/gpio/gpio-sifive.c

@@ -267,4 +267,8 @@ static struct platform_driver sifive_gpio_driver = {
 		.of_match_table = sifive_gpio_match,
 	},
 };
-builtin_platform_driver(sifive_gpio_driver)
+module_platform_driver(sifive_gpio_driver)
+
+MODULE_AUTHOR("Yash Shah <yash.shah@sifive.com>");
+MODULE_DESCRIPTION("SiFive GPIO driver");
+MODULE_LICENSE("GPL");