gpio/sifive: Add GPIO driver for SiFive SoCs

Adds the GPIO driver for SiFive RISC-V SoCs.

Signed-off-by: Wesley W. Terpstra <wesley@sifive.com>
[Atish: Various fixes and code cleanup]
Signed-off-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Yash Shah <yash.shah@sifive.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/1575976274-13487-6-git-send-email-yash.shah@sifive.com
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 6ab25fe..809dd54 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -479,6 +479,15 @@
 	  The difference from regular GPIOs is that they
 	  maintain their value during backup/self-refresh.
 
+config GPIO_SIFIVE
+	bool "SiFive GPIO support"
+	depends on OF_GPIO && IRQ_DOMAIN_HIERARCHY
+	select GPIO_GENERIC
+	select GPIOLIB_IRQCHIP
+	select REGMAP_MMIO
+	help
+	  Say yes here to support the GPIO device on SiFive SoCs.
+
 config GPIO_SIOX
 	tristate "SIOX GPIO support"
 	depends on SIOX