ARM: mxs: select SPARSE_IRQ

With icoll and gpio interrupt controllers adopt irqdomain support and
all interrupt nubmers are retrieved from device tree, it's safe to
select SPARSE_IRQ for mxs now.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/Kconfig

@@ -491,6 +491,7 @@ config ARCH_MXS
 	select HAVE_CLK_PREPARE
 	select MULTI_IRQ_HANDLER
 	select PINCTRL
+	select SPARSE_IRQ
 	select USE_OF
 	help
 	  Support for Freescale MXS-based family of processors