gpio/mxs: convert gpio-mxs to use generic irq chip

The patch converts gpio-mxs driver to use generic irq chip.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 531bfb6..b84666a 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -102,6 +102,7 @@
 	def_bool y
 	depends on ARCH_MXS
 	select GPIO_GENERIC
+	select GENERIC_IRQ_CHIP
 
 config GPIO_PLAT_SAMSUNG
 	def_bool y