mfd: max77686: Convert to use regmap_irq

By using the generic IRQ support in the Register map API, it
is possible to get rid max77686-irq.c and simplify the code.

Suggested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Tested-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index b8d9ca0..3010204 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -384,6 +384,7 @@
 	depends on I2C=y
 	select MFD_CORE
 	select REGMAP_I2C
+	select REGMAP_IRQ
 	select IRQ_DOMAIN
 	help
 	  Say yes here to add support for Maxim Semiconductor MAX77686.